that's___the Party called on us to do.A that B what C how D why 选哪个?是什么从句?

问题描述:

that's___the Party called on us to do.
A that B what C how D why
选哪个?是什么从句?

what 那是党号招我们要做的

B what
表语从句
是党叫我们这样做的.