Q16:

While digging in the Egyptian desert, huge fossil bones have been found by paleontologists, which appears to have been the second most massive dinosaur that ever lived.

1. huge fossil bones have been found by paleontologists, which appears to have been
2. huge fossil bones have been found by paleontologists, which appear to be from
3. it appears that paleontologists have found huge fossil bones that are from
4. paleontologists have found huge fossil bones from what appears to be
5. paleontologists have found huge fossil bones, which are from what appear to be

不太明白d中的what的用法,该怎么理解,e为什么不对

what和which、that不一样，不是关系代词，不能引导从句。你大多数情况可以直接把它看成一个名词，在这里直接作主语。