With the help of high technology, more and more new substances____in the past years.
| A．discovered | B．have discovered | C．had been discovered | D．have been discovered |
. — He speaks French because he once lived in France.
—Really? How long _____ there?
| A．does he live | B．was he living | C．has he lived | D．did he live |
. — We had a good time in the park last Saterday. Pity you weren’t there.
— I really ____ come but I was looking after my mother in the hospital.
| A．must | B．ought to | C．need have | D．should have |
. Why not try your luck downtown? That’s ____ the best jobs are.
| A．where | B．what | C．when | D．why |
. _____ with letters and public phones, mobile phones and the Internet are faster and much more convenient.
| A．Compare | B．To compare | C．Comparing | D．Compared |
. The little boy is dirty from head to foot because he ___ in the mud all morning.
| A．had played | B．has played | C．was playing | D．is playing |