单项选择题

In this research at Columbia University, Charles Townes worked with ______.

A．stimulated emission
B．microwaves
C．maser
D．stimulated emission and microwaves
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单项选择题
According to the passage, which of the following is TRUE of male dik-dik
A．He can in principle defend more than one female.
B．He practices monogamy.
C．He invests heavily in his offspring.
D．He is partly monogamous and partly polygamous.
单项选择题
We can infer that the chance for female marmoset and tamarin monkeys to have twin births depends on ______.
A．the number of male they have access to
B．the workload they have in bringing up the young
C．the time when they come into estrus
D．the size of the males' bodies
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