When will the expert come and give the lecture one conomic development?Not until our program A.is approvingB.is to approveC.has been approvedD.wil lbe approved选C,但是为什么选C

When will the expert come and give the lecture one conomic development?Not until our program A.is approvingB.is to approveC.has been approvedD.wil lbe approved选C,但是为什么选C
When will the expert come and give the lecture one conomic development?
Not until our program
A.is approving
B.is to approve
C.has been approved
D.wil lbe approved
选C,但是为什么选C

When will the expert come and give the lecture one conomic development?Not until our program A.is approvingB.is to approveC.has been approvedD.wil lbe approved选C,但是为什么选C
Not untill意思是“直到”,后面要跟现在完成时.

您好！我目前持有剑桥商务英语BEC高级和英语专业八级证书，我的理解如下：
中文意思为“直到我们的项目被证实后才来吗？”
请留意“被证实后”
由此可知用被动完成时。
若仍不理解，欢迎继续追问大家相互探讨，谢谢。