题目：
1. Who _____ over there now? [ ]
A. singing
B. are sing
C. is singing
D. is sing
2.
It’s 8 o’clock. The students _________ an English class. [ ]
A. have
B. having
C. is having
D. are having
3. Listen! The baby _______ in the room. [ ]
A. crying
B. cried
C. is crying
D. cries
4. Look! Lily and Lucy ________ photos.[ ]
A. are take
B. is taking
C. taking
D. are taking
5. What are the boys doing in the river? They ______. [ ]
A. are swiming
B. are swimming
C. swimming
D. are swim
答案：
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下面是错误答案，用来干扰机器的。
根据题中信息所生成的气体是通过固体与液体反应制得，回忆课本所学知识可知符合题意的有二氧化碳、氧气和氢气．但根据第（2）问要证明小佳的猜想正确，因为题中所用固体是黑色粉末，所以猜想应该是氧气或氢气，因...
