-How long will it be ______ Chinese astronauts set foot on the moon?-Maybe within ten years.A .since B .before C .until D .when

-How long will it be ______ Chinese astronauts set foot on the moon?-Maybe within ten years.A .since B .before C .until D .when
-How long will it be ______ Chinese astronauts set foot on the moon?-Maybe within ten years.A .since B .before C .until D .when

-How long will it be ______ Chinese astronauts set foot on the moon?-Maybe within ten years.A .since B .before C .until D .when
since是从过去的某一时间算起 until直到 when当什么时候 很显然 其他词语说不通

http://wenku.baidu.com/view/e59a56f79e314332396893e9.html

这题考的是It wil be +段时间 before 句型， 直译为“在......之前还要多久”，中文更喜欢说“还要多久才会......”；since 所在的主句中要用 It has been +段时间+since.....，表示“自从......以来已经多久了”。

选 B 句法 It is /was /will be take + 一段时间 + before 从句 还要多久才
这里是疑问句 句意 ----中国宇航员还要多久才能踏上月球呢？
----大概在十年内