Speciation,__________, results when an animal population becomes isol-考呗网题库移动版

单选题 Speciation,__________, results when an animal population becomes isolated by some factor, usually geographic.

A．form biological species
B．biological species are formed
C．which forming biological: species
D．the formation of biological species

参考答案D

解析:

单选题 __________in the United States, St. Louis has now become the 24th largest city.

A．The fourth biggest city it was
B．Once the fourth biggest city
C．Being the fourth biggest city
D．It was once the fourth biggest city

单选题 He said it was impossible for__________a mistake in a computer's calculation, so you can rely on that.

A．there being
B．there would be
C．there to be
D．there was

单选题 Contrast may make something appear more beautiful than it is when__________ alone.

A．seen
B．is seen
C．to be seen
D．having been seen