单项选择题

Sulphur has occasionally been found in the earth in an almost pure state.

A．regularly
B．accidentally
C．sometimes
D．successfully
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单项选择题
Techniques to harness the energy of the sun are being developed.
A．convert
B．store
C．utilise
D．receive
单项选择题
When doves are about two weeks old, they are covered with grey feathers and are ready to try their wings.
A．grow
B．wrap
C．hide
D．test
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