most of the world surface is water. we may (1).........the land very well,but we know very little about the ocean . until recently, man could not (2)............underwater for long. but now, with special breathing equipment, a diver can swim longer. after the (3)................of this equipmen , man could swim freely underwater and scuba-diving became a popular sport. we can lean more about the undersea world thanks .......(4)...........this invention.

1.A. knew          B.to know       C.knowing           D.know

2.A. to stay       B.stayed          C.stay                  D. staying

3.A. invent        B. invention      C.invented           D.inventing

4.A.for               B.on                 c. with                  D.to

1.he is a slow and careful driver

he driver......................

2.I spend two hours a day doing my homework

it takes me.....................

it is