我怎么就理不顺这个句子?The Bunsen Burner is so named because it is thou

Hi
这样,把这个复合句拆开,先从because分成两大块.because引导一个原因状语从句,前面的就不用管了.it is thought 是一个被动语态,后面可以跟宾语从句也可以跟to do不定式结构（和 it is believed,it is considered 一样）.
故可排除选项B和C.若答案仍选的是D,则说明本句还是要强调发明本森灯这件事发生在前.
原句若省略it is thought,则变为it has been invented.加上 it is thought后则变为 it is thought to have been thought.
不知道我说清楚了没有?

b

Robert Bunsen is thought to have invent it.
It is thought to have been invented by Robert Bunsen.
D