单项选择题

A．only a limited number of chimpanzees are used for sam……

Many AIDS experts are not completely satisfied with results of the study because _______.

A．only a limited number of chimpanzees are used for sampling the virus
B．it is now extremely difficult to find chimpanzees that carry the virus
C．the samples collected are from two different subspecies of chimpanzees
D．it does not provide reliable evidence of the link between SIV and HIV-I

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单项选择题What is exceptionally remarkable about a child is that ______.

A．he is born with the capacity to speak
B．he has a brain more complex than an animal's
C．he can produce his own sentences
D．he owes his speech ability to good nursing

单项选择题The purpose of Frederick I's experiment was _______.

A．to prove that children are born with the ability to speak
B．to discover what language a child would speak without hearing any human speech
C．to find out what role careful nursing would play in teaching a child to speak
D．to prove that a child could be damaged without learning a language

单项选择题Which of the following can NOT be inferred from the passage

A．The faculty of speech is inborn in man.
B．Encouragement is anything but essential to a child in language learning.
C．The child's brain is highly selective.
D．Most children learn their language in definite stages.