语法老师请进,
1.The captian knew that _____ the only sttempt.
A.his would not be B.it had not been.
2.It was a ship which had been sunk many years ____ in fact found.
A.that they had B.which was .
上面的答案分别是A ,A .那么另外另外两个答案为什么不对呢?