朋友.答案错了,应该是 Rarely seen.
1 B.Rarely to be seen 强调的是一种“目的”概念,在这里与句子的逻辑不符合,所以是错的.
2 C.Rarely seen是正确的答案,做句子主语 the white mountain goat 前置定语,具体解释就是:The white mountain goat,WHICH IS RARELY SEEN,is an extremely sure-footed - - - .
3 如果是Rare to be seen的话,也是对的,这样就等于:WHICH IS RARE TO BE SEEN.