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单项选择题

A．the methods used of blood-cell calculation are not ac……

According to the passage, DNA fingerprinting can be unreliable when ______.

A．the methods used of blood-cell calculation are not accurate
B．two different individuals of the same ethnic group may have the same DNA fingerprinting pattern
C．a match is by chance left with fingerprints that happen to belong to two different individuals
D．two different individuals leave two DNA samples
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单项选择题To geneticists like Lewontin and Hartl, the current method ______.

A．is not so convincing as to exclude the likelihood that two DNA samples can never come from two individuals
B．is beyond dispute because two individuals of the same ethnic group are likely to have the same DNA pattern
C．is not based on adequate scientific theory of genetics
D．is theoretically contradictory to what they have been studying

单项选择题The National Academy of Sciences holds the stance that ______.

A．DNA testing should be systematized
B．only authorized laboratories can conduct DNA testing
C．the academy only is authorized to work out standards for testing
D．the academy has the right to accredit laboratories for DNA testing

单项选择题We learn from the passage that ______.

A．foreign language requirements for the Ph. D. do not vary in difficulty among universities
B．meeting foreign language requirements for the Ph. D. is the most frequent reason for dropping out
C．it is an essential part of many Ph. D. programs to meet foreign language requirements for the Ph.D.
D．meeting foreign language requirements for the Ph. D. is more difficult for the science candidate than for the humanities candidate

单项选择题It can be inferred from the passage that ______.

A．there are 1,000 positions for the Ph. D. s
B．the high rate of dropouts is because the salary for dropouts is too high
C．the high rate of dropouts lies in the fact that the salary for Ph. D. is too low
D．the reason why so many Ph. D. candidates drop out is that academic requirement is too high for them

单项选择题Research has shown that ______.

A．Dropouts are substantially below Ph. D. s in financial attainment
B．the incentive factor is a minor one in regard to pursuing Ph. D. studies
C．the Ph. D. candidate is likely to change his field of specialization if he drops out
D．about one-third of those who start Ph. D. work do not complete the work to earn the degree