题目

Yao Ming, a basketball giant , ___________ water polo when he was young.A. is playing B. used to play C. is used to playing D. was playing 答案：【答案】B【解析】句意：姚明，一个篮球巨人，小时候经常打水球。is playing正在玩，现在进行时；used to play过去常常玩；is used to playing习惯于玩…；was playing过去进行时。根据句意when he was young可知，这里说的是过去的事情，故应选B。 氧化剂和还原剂：在氧化还原反应中，所含元素的化合价________的反应物称为氧化剂；所含元素的化合价________的反应物称为还原剂．