known to be 是不是永远错，比较大全449和大全705

大全449

 It may be another fifteen years before spacecraft from Earth again venture to Mars, a planet now known to be cold, dry, and probably lifeless.
(A) again venture to Mars, a planet now known to be
(B) venture to Mars again, a planet now known for being
(C) will venture to Mars again, a planet now known as being
(D) venture again to Mars, a planet that is known now to be
(E) will again venture to Mars, a planet known now as being

答案A

大全705

49. The cameras of the Voyager II spacecraft detected six small, previously unseen moons circling Uranus, which doubles to twelve the number of satellites now known as orbiting the distant planet
            

(A) which doubles to twelve the number of satellites now known as orbiting
            

(B) doubling to twelve the number of satellites now known to orbit
            

(C)
                which doubles to twelve the number of satellites now known in orbit around
                    

(D) doubling to twelve the number of satellites now
            known as orbiting

(E) which doubles to twelve the number of satellites
                now known that orbit

答案B

在白勇的书里说

正确用法：know as +n. 或者known to do (但known to be 永远错）

那么上面的大全449为什么是对的呢，还是答案错了，谁有语法书能查到这个known的用法呢？

谢谢。

known as/for/to do sth

Here's how we should use these:

1. Known to do something: Usually, we say "known to do sth" in two different ways. First, when we want to talk about some fact that people have learned. We also use this when we are talking about the habits of someone or someting that other people know about.