___is still unknown when we can finish this project.a,it.b,that.c_英语解答

___is still unknown when we can finish this project.
a,it.b,that.c,which.d,this.

人气：252 ℃　时间：2019-10-23 13:11:30

解答

a it 形式主语 when we can finish this project is still unkown
it指代when we can finish this project