81. Fossils of the arm of a sloth found in Puerto Rico in 1991, and dated at34 million years old, made it the earliest known mammal of the Greater Antilles Islands. (A) sloth found in Puerto Rico in 1991, and dated at 34million years old, made it the earliest known mammal of (B) sloth, that they found in Puerto Rico in 1991, hasbeen dated at 34 million years old, thus making it the earliest mammal known on (C) sloth that was found in Puerto Rico in 1991, wasdated at 34 million years old, making this the earliest known mammal of (D) sloth, found in Puerto Rico in 1991, have been datedat 34 million years old, making the sloth the earliest known mammal on (E) sloth which, found in Puerto Rico in 1991, was datedat 34 million years old, made the sloth the earliest known mammal of
答案是D 包子不明白 为什么要用完成时 是说过去的发现 对现在有影响吗 但是句子里没有现在 时间的表现
还有 making the sloth...是结果还是伴随状语噶
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