Not until __________ on TV __________ that the Chinese ship was rescued by the European Union Task Force.

A．did I turn; did I know

B．did I turn; I knew

C．I turned; did I know

D．I turned; I had known

 研究表明，许多金属氧化物对氯酸钾的分解有催化作用。下表是不同金属氧化物作催化剂，氯酸钾剧烈反应时的温度，实验室用氯酸钾制取氧气时，如不用二氧化锰作催化剂，最好选用：

A．氧化铁

B．氧化铝

C．氧化铜

D．氧化镁