11 错误,他们学习并互相帮助
12 错误,Her Chinese is better than mine.
13 正确
14 错误,Thirty-five divided by five is seven.
15 错误,Bus number 4
16 错误,Robert said he has been joking with Mary.
17 正确
18 错误,There is some milk in the bottle, isn't there?
19 错误,He stayed in his room and played the computer games.
20 正确