One of the most important problems they had to consider was________of public health.

— How many classmates did you see there?— ________.

Annoyed by the salesman's bad manner，John chose ________of the two computers on sale and left.

______ is important to know how to get on with others when you grow up.

—What about asking these new graduates to take on the task?—I m afraid not．While they are energetic and ambitious, _____ of them seems to be suitable for this demanding job．