挑战英语语法问题 被动语态

挑战英语语法问题 被动语态
1.To understand the situation completely requires more thought than _____________________.
a.has given b.has been given c.had given d.had been given
为什么,请详解,该句比较级如何理解.
2.THe main stream of a river frequently _________ into two or more branches near its mouth.
a.divides b.is divided
为什么?难道我们上课经常说 the passage is divided into three paragraphs 一直是错的吗?
3.These minerals are known _____________ on the moon.
a.to have been collected b.to be collected
为什么,赶紧b也对呢