题干
— Must I sing the song Live It Up at the party next weekend?
— No, you ________. You ________ sing others like You Raise Me Up.
A：can't; must
B：mustn't; can
C：may not; must
D：needn't; may
答案(点此获取答案解析）
D
CO2+H2，当反应达到平衡时，CO的体积分数为W，若维持容器的体积和温度不变，起始物质按下列四种配比充入该容器中，达到平衡时CO的体积分数小于W的是（ ）