He didn't attend class today, I guess he __________ have caught a cold again.
. One third of the area ______ covered with trees. About seventy percent of the trees ______ been planted recently.
Nowadays teens prefer going to the net-bar ______ they can chat with their friends by QQ or play computer games ______ some more reading.
It has been announced that all the students ______ put on the masks before going to school in case they are infected with SARS virus.
Some researchers are finding that daydreaming may be important to ______ mental health. Daydreaming, they say, is _____ good means of relaxation.
--- How long do you think it’ll be ______ I can go back to work?--- Well, you’ll be feeling better by next weekend.