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Some of the following sentences have mistakes. Find the sentences and correct the mistakes.
1) I thought a lot but couldn't remember his name. 2) Was he able to talk to his
neighbour? 3) I couldn't do the sums myself and asked my father to help me.
4) They could play their parts so well that the audience broke into laughter
again and again. 5) How did you manage to do all that work on your own?
6) I could answer the teacher's question and was very proud of myself. 7) The
children couldn't go to the beach as it was raining. 8) Sally could win the
100-metre race. 9) At last we could see the film we had wanted to see so long.
10) Why couldn't he explain the problem more clearly?