现在完成时专项练习题及答案一、 单项选择。1、Both his parents look sad . Maybe they _whats happened to him . . knew . have known . must know .will know 2、He has _ been to Shanghai , has he ? . already .never .ever . still 3、Have you met Mr Li _? . just . ago .before . a moment ago 4、The famous writer _ one new book in the past two year . . is writing