题干
By the time I ________ on the TV, Beckham ________ two goals．
A：turned; have scored
B：turned; had scored
C：had turned; have scored
D：had turned; had scored
答案(点此获取答案解析）
B
2SO3(g)经一段时间后，SO3的浓度增加了0.4 mol/L，在这段时间内用O2表示的反应速率为0.04 mol/(L·s)，则这段时间为( )
