22、--Sorry．I made a mistake again．

--________．Practice more and you'll succeed．

A．Never mind                               B．Certainly not

C．Not at all                                   D．Don't mention it

21、It's the second time that I ________ to Shanghai．It's ten years since I ________ it last time．

A．have been；left         B．had been；left       C．am；had left            D．come；had left

20、The message is very important，so it is supposed ________ as soon as possible．

A．to be sent             B．to send          C．being sent               D．sending

19、Einstein like Bose's paper so much that he ________ his own work and translated it into German．

A．gave off          B．turned down          C．took over                  D．set aside

18、I like getting up very early in summer．The morning air is so good ________．

A．to be breathed           B．to breathe           C．breathing             D．being breathed

17、The country has already sent up three unmanned spacecraft，the most recent ________ at the end of last March．

A．has been launched                             B．having been launched

C．being launched                                    D．to be launched

16、At the beginning of class，the noise of desks ________ could be heard outside the classroom．

A．opened and closed                                   B．to be opened and closed

C．being opened and closed                           D．to open and close

15、The steam engine gives us an example of heat ________ into work．

A．turns            B．turned            C．turning                 D．being turned

14、It is strongly recommended that the machine ________ until it has been fully checked．

A．is not used                                                B．will not be used

C．not be used                                               D．is not to be used