51. Though Jane tried her best this time, but she still failed in the math exam.
解析:虽然这次简尽力了,但是她这次数学考试仍然考砸了。
汉语中用虽然…但是…,但是在英语中,though和but不能同时用,用一个就能表示虽然…但是…的含义。所以选择C,把but去掉。正确的句子应该是Though Jane tried her best this time, she still failed in the math exam.或者Jane tried her best this time, but she still failed in the math exam.