The father advised her to avoid the mistake made by many couples of marrying for the wrong reasons（）he found the young man charming and intelligent.

单项选择题There have been many（）in their marriage but they still love each other.

A.ups and downs
B.from head to toe
C.time and again
D.over and over

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

A.consistent
B.continual
C.continuous
D.numerous

单项选择题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

单项选择题We watched the plane（）behind the clouds.

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

单项选择题Pipes made of plastic are now widely used in building as they are light and do not become （）in water.

A.ripe
B.instant
C.rotten
D.mature