How unhappy your roommate looks!—-Yes，but he’s not willing to tell me what it is____ is troubling him.

Do you know him—I’m sure I’ve seen him _____, but I can’t remember the right place.

When we go to bed ,our parents often say to us.

he problem of land erosion getting moreserious, the government is searching for a way to deal withit

Is the math problem ______– Yes, I can work it out ______.