it ------- be difficult to learn it.have you triedA shall B must C should D need

问题描述:

it ------- be difficult to learn it.have you tried
A shall B must C should D need

B must
学习它一定很难吧,你试过了吗?

it is difficult to learn it.have you tried?
学习这很难 你累了吗?

B
表猜测用must