Read the passage and then choose the best option to fill in each of the blanks below. Most of the world’s surface is water. We may (26)_____the land very well, but we know very little about the ocean. Until recently, man could not (27)_____underwater for long. But now, with special breathing equipment, a diver can (28)_____longer. After the invention of this equipment, man could (29)_____freely underwater and scuba-diving became a popular sport. We can (30)_____more about the undersea world thanks to this invention. 26. A. knew B. to know C. knowing D. know 27. A. to stay B. stayed C. stay D. staying 28. A. staying B. stay C. to stay D. stayed 29. A. swim B. swimming C. swam D. to swim 30. A. learning B. learned C. to learn D. learn