用适当的介词填空

①As a student, you should focus ____ your school work rather than some other things.

②Working in so much noise can cause damage ____ your hearing.

③His laziness and carelessness led ____ his failure in the examination.

④I am still a little confused____ what happened.

⑤I don’t want to make comments  ____ other people’s privacy.

已知一个正数的平方根分别是2a﹣7与﹣a+2，求这个数．

Mr. Hu____ ____ having a rest in his bedroom.