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26.Is ______ necessary to tell his father everything?A.It B. that C. what D. he27.______ must be something wrong with the machine.A.There B. It C. He D. That28.______ is known to us all, the earth turns around the sun.A. It B. Which C. As D. That29.______ is known to us all that the earth turns around the sun.A.It B. Which C. As D. That30.______ is difficult to persuade her to stay.A.It B.What C. He D. That31.______ is difficult is to persuade her to stay.A.It B. What C. He D. That32._______ seems to be a strong competition in China for senior high students to enter college or university.A. It B. Which C. What D. That33.I know you don't like her, but try not to make ________ so obvious.A. This B. her C. it D. one34.I have a lot of books, ha