单项选择题

Earthworms occur ______ adequate moisture and food and the necessary soil conditions are found.

A．and
B．whenever
C．however
D．wherever
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单项选择题
The first ______ in the development of civilized man were probably the invention of primitive weapons and the discovery of fire.
A．intervals
B．breaks
C．stages
D．periods
单项选择题
An old friend from abroad, ______ I was expecting to stay with me, telephoned from the airport.
A．that
B．which
C．whom
D．who
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