单项选择题

Silk worms and bees are ______ , while flies and mosquitoes are ______.

A．beneficial insects... pests
B．pests... beneficial insects
C．harmful to people... helpful to people
D．helpful to people... helpful to people too
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单项选择题
Which of the following is not true
A．When they grow up, insects look the same as when they are young.
B．Insects keep changing during their growth.
C．Insects have different shapes.
D．Not all insects look the sam
单项选择题
What is the important insight recently gained in the study of E1 Nino
A．E1 Ninos are usually accompanied by warm currents.
B．E1 Ninos are destructive.
C．La Ninas come between E1 Ninos.
D．La Ninas are less destructive than E1 Ninos.
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