单项选择题

The main boyhood (interesting) of (psychologist) Jean Piaget (was) the observation of animals (in their) natural habitat(栖息地).（）

A.interesting
B.psychologist
C.was
D.in their

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单项选择题

Birds (whose) coloring blends in with the leaves (do not) seen (as easily as) (those) with brighter feathers.（）

A.whose
B.do not
C.as easily as
D.those

单项选择题

A cartel is (an association) of producers in a (given) industry (whose) purpose is (restrict) competition.（）

A.an association
B.given
C.whose
D.restrict

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