15．You may ________ the textbook if you don’t know the answer to the question.

Ten years ago the population of our villagewas________that of theirs.

_________ from your family and friends, though it may cause short-term discomfort, doesn’t have to be as painful as it seems.

he saw Zhao Benshan’s funny performances, he burs into laughter

d he had called me to returnhome, but I didn’t receive _________.