(1)From the results section of an experimental report:
Figure 2______(shows/showed/has shown) the current-voltage (Ⅰ-Ⅴ) characteristics of aluminum contacts on boron-doped polycrystalline diamond films deposited from gas mixtures with different concentrations of boron． The I-V characteristics______(are/were/have been)determined by applying a voltage to the A1 contact on the diamond film surface while grounding the rear of the Si substrate． Poor rectifying characteristics______(are/were/have been) obtained as a result of excess reverse leakage current． When the boron concentration______(increases/increased/has increased), the forward current______(decreases/decreased/has decreased)． This decrease in the forward current______(may be/was/has been) attributed to impurity scattering on the diamond film． For a given temperature, the mobility______(decreases/decreased/has decreased) with increasing impurity concentration because of enhanced impurity scattering． The smaller forward current______(is/was/has been) due mainly to the smaller hole and electron mobility．
Figure 3______(shows/showed/has shown) the I-V characteristics of diamond films deposited with various boron concentrations and annealed at a constant temperature in helium ambient at 900 ℃for 30 min． After the annealing treatment, there______(is/was/has been) no deterioration in the I-V characteristics of the undoped films． In the boron-doped films, the leakage current for the 10 V forward voltage______(doubles/doubled/has doubled) and deterioration in the rectifying characteristics______(is/was/has been) observed．
(Adapted from work by Chia-fu Chen and associates, National Chiao Tung University,Taiwan．)
(2)From the introduction to a research report:
For many years now, kinship______(is/was/has been) recognized as an important factor in human social behavior, and recent studies______(are demonstrating/have demonstrated/had demonstrated) that kinship______(influences/influenced/has influenced) the social behavior of many other species as well． The widespread occurrence of nepotism, or favoritism shown to genetic relatives, and the rarity of close inbreeding among free-living animals______(imply/implied/have implied) that most animals ______( possess/possessed/have possessed)mechanisms for distinguishing relatives from nonrelatives and close from distant kin．
However, until the last few years little attention________(is/was) paid to mechanisms of kin identification． In this paper, we______(consider/considered/have considered) some of the theoretical and empirical issues relevant to animal kin recognition,______(describe/described/have described) recent work on this topic, and______(outline/outlined/have outlined) several mechanisms by which kin might be identified． Finally, we(summarize/summarized/have summarized) the results of our four-year laboratory and field investigation of kin recognition using ground squirrels．(www.xing528.com)
(Adapted from Warren G． Holmes and Paul W． Sherman, Kin recognition in animals,American Scientist, Vol．71,1983,p．46)
(3) Maps and Computers:
Maps______(are/were/have been) one of the oldest forms of written communication． Land boundary maps on clay tablets______(are being/were being/had been being) used in Babylonia as early as 2200 B．C．Through the centuries various materials______(are/were/have been) used for maps． The ancient Egyptians______(use/used/had used) sheets of papyrus, the Chinese______(use/used/had used) pieces of silk． Eskimos______(make/made/had made) maps on sealskins, and Polynesians______(use/used/had used) a network of bamboo canes, with each crossing point indicating an island． Today printed maps______(pervade/pervaded/have pervaded) our lives, ranging from sketch or location maps in newspapers and advertisements, to parcel maps showing property boundaries, to small-scale maps in atlases．
The techniques used to produce maps______(changes/changed/have changed) dramatically over the past fifty years,in a transition from field workers and mule trains to jet aircraft,satellites,and computers． Before World War Ⅱ,the predominant method for creating maps______(is/was/has been) field surveying． After World War Ⅱ, map-making methods______(begin/began/have begun) to include manual photogrammetry (measurement from photographs)．Although manual photogrammetry______(is/was/has been) still used today, it______(is being/was being/had been) supplanted by digital cartography, and computers______(are/were/had been) becoming the hub of the mapping process．
Soon after their introduction in the 1950s, digital computers______(are/were/have been)used for various phases of the mapping process, especially for trigonometric calculations of survey data and for orientation of aerial photographs on map manuscripts． In addition, computercontrolled plotters______(are/were/have been) used to draw simple outline maps． The process of collecting data for the plotters______(is/was/has been) slow and expensive, and the drawings______( are/were/had been) not as precise as those produced by the best manual cartography． Only in the last ten to fifteen years______(does/did/has) it become technologically feasible and cost-effective to assemble and use the data required to automate the mapping process．
(Adapted from Steven C． Guptill and Lowell E． Starr． Making maps with computers．American Scientist． Vol．76,1988,P:136-137)
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