[求助]再请教GWD-29-7

Until a few centuries ago, any large bones discovered in the fields or caves of Europe, now known to be large prehistoric animals, were usually assumed to be the remains of giants and were often displayed as curiosities in castles, palaces, town halls, churches, and monasteries.

1. now known to be large prehistoric animals, were usually assumed to be
           
2. presently known as from large prehistoric animals, were usually assumed as
           
3. bones now known to be those of large prehistoric animals, were usually assumed to be
           
4. bones known at present as of large prehistoric animals, were usually assumed as those of
           
5. currently known as those of large prehistoric animals, were usually assumed to be those of

ABE都很容易排除，但是C和D有点confusing，but the answer is C,请问：

1。C中的known to be those of中的those 代表bones,在作同位语时bones已经补出，为什么这里还要再来一个those呢？

2。C中的后半部分，were usually assumed to be
        remains
        of giants, 这里的those却又不用补出了，是不是bones=remains?

3。在C和D的比较中，known to be和known as 有决定意义吗？个人觉得两者都对。

4。assume to be和assume as呢？

问题真的好多，谢谢指教！

C those of还是要加上的

A的排除就是把骨头当成了动物