单项选择题

Which of the following statements best describes a laser

A．A device for stimulating atoms and molecules to emit light.
B．An atom in a high-energy state.
C．A technique for destroying atoms or molecules.
D．An instrument for measuring light waves.

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单项选择题

Why was Townes' early work with stimulated emission done with microwaves

A．He was not concerned with light amplification.
B．It was easier to work with longer wavelengths.
C．His partner Schawlow had already begun to work on laser.
D．The laser had already been developed.

单项选择题

According to the passage, male marmoset and tamarin monkeys ______

A．can't defend more than one female
B．practice monogamy
C．get more offspring
D．invest heavily in their partners and the young