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).
单项选择题 The United Nations Conference on Global Environment, which took place earlier this year in Vienna, was a very（） meeting.
单项选择题 We watched the plane（）behind the clouds.
