The research mainly deals with the difficulty the students have ______ their attention pm their study all the time.
| A．to focus | B．to be focused | C．focusing | D．focused |
The how-to book can be of help to ______ wants to do the job.
| A．who | B．whomever | C．no matter who | D．whoever |
---Is Bob still performing?
--- I’m afraid not. He is said _____ the stage already as he has become an official.
| A．to have left | B．to leave | C．to have been left | D．to be left |
______ with so much trouble, we failed to complete the task on time.
| A．Faced | B．Face | C．Facing | D．To face |
________ , some famous scientists have the qualities of being bothe careful and careless.
A Strangely enough B Enough strangely C Strange enough D Enough strange
Paper money was in ______ use in China when Marco Polo visited in ____ thirteen century.
| A．the;/ | B．the, the | C．/, the | D．/, / |