题干
The children are having fun _________ on the beach（海滩）.
A：play
B：plays
C：played
D：playing
答案(点此获取答案解析）
D
The children are having fun _________ on the beach（海滩）.
A：play
B：plays
C：played
D：playing
2SO3，改变下列条件，可以提高反应物中活化分子百分数，但不改变SO2的转化率的是( )
