An even more exciting find was reported in 1994, also from Pakistan. The now extinct whale Ambulocetus natans(the walking whale that swam) lived in the Tethys Sea 49 million years ago. It lived around 3 million years after Pakicetusbut 9 million before Basilosaurus.The fossil luckily includes a good
portion of the hind legs. The legs were strong and ended in long feet very much like those of a modern pinniped. The legs were certainly functional both on land and at sea. The whale retained a tail and lacked a fluke, the major means of locomotion in modern cetaceans. The structure of the backbone shows, however, that Ambulocetus
swam like modern whales by moving the rear portion of its body up and down, even though a fluke was missing. The large hind legs were used for propulsion in water. On land, where it probably bred and gave birth, Ambulocetusmay have moved around very much like a modern sea lion. It was undoubtedly a whale that linked life on land with life at sea.

11. The word propulsion in the passage is closest in meaning to

o staying afloat
o changing direction
o decreasing weight
o moving forward

猜词义:可以用排除法。显然weight, direction原文中没有提到。前面一句提到moving, 所以moving forward 是最佳答案。