The local government tried its best to ensure each of its citizens a（）supply of food at regular intervals (时间间隔).

The United Nations Conference on Global Environment, which took place earlier this year in Vienna, was a very（） meeting.

A.productive
B.communicative
C.aggressive
D.protective

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We watched the plane（）behind the clouds.

A.disappearing
B.disappeared
C.diving
D.dived

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