.It is _____that he has been addicted to thedrugs and has difficulty quitting it.

The oldman has three sons，and two_____ are doctors．

k God! The accident was avoided after all.—That was lucky, but ten inches nearer the two cars_________

future, care for the environmentwill become very important as earth’s natural resources _____

For our middle school students, some courses are compulsory, while others are ________.