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 答案选b 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 答案是a 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答案选c 为什么，赶紧b也对呢