填空。 Do you like Dolphins (海豚)? Dolphins live 1 water, but they are not fish. They are mammals (哺乳 动物) that live in water. It has to (不得不) breathe (呼吸) air to the top of the water very often. A dolphin's nose isn't 2 to see. It's just a very 3 hole on top of the dolphin's head. This hole is called a blowhole. A dolphin 4 up every minute or so to breathe. It opens blowhole and takes air in, and then goes back into the water again. It can stay 5 the water for six or seven minutes if it has to. A dolphin's ears are very small, 6 its mouth is very 7 . It has almost one hundred teeth. A dolphin 8 very fast. Scientists are studying ways to 9 boat go faster through the 10 . (     )1.A. in (     )2.A. easy (     )3.A. small (     )4.A. goes (     )5.A. at (     )6.A. if (     )7.A. small (     )8.A. goes (     )9.A. make (     )10.A. air B. on B. difficult B. big B. comes B. up B. or B. big B. swims B. ask B. room C. above C. good C. smaller C. walks C. on C. but C. good C. runs C. tell C. land D. under D. fast D. bigger D. runs D. under D. so D. nice D. walks D. talk to D. water