“这个问题很难回答”用英语怎么说

Question

练习册上有一个句子写“the question is difficult to answer”，但是选择题的答案却是“the question is difficult to be answered”。
正确的应该是前一句吧？？

Answer 1

this question is difficult to answer.

Answer 2

this question is difficult to answer.

Answer 3

It is too difficult to answer this question.

Answer 4

It's very hard/difficult to answer the question.

Answer 5

This question is difficult to answer.

Answer 6

this question is difficult to answer