This book is not_______for a six-year-old child to read.

It is           to cycle around Guilin．

His mother says, “Listen to me __________. Make sure to be __________ with matches.”

---Have you returned the book to the library ____?   ---Yes, I have ____ returned it.

—What do you think of the report about the air pollution on TV last night?—I think the situation is so        that we should take action to protect the environment.