The book,_______________as a surprise for his sister was lost in the mail.
| A．intended | B．to be intended | C．Intending | D．being intended |
.Getting to other planets or to the moon _____ many problems.
| A．involve | B．involves | C．involving | D．to involve |
.In that country, the rich ______ richer, the poor, poorer.
| A．become | B． has become | C．becomes | D．is becoming |
.The project requires more labor than ______ because it is extremely difficult.
.Not one in one hundred children exposed to the disease ______ likely to develop it.
| A．should be | B．must be | C．is | D．are |
Robert is said ______ abroad，but l don't know what country he studied in．
| A．to have studied | B．to study | C． to be studying | D．to have been studying |