北京周边背包游:几道英语单选题

1．We try to point out that no matter of stage of life you may be in ----young, middle-aged or retired-------there’s___possibility of a_____constantly expanding field of interest,excitement,challenge,fulfillment and adventure.
A.a a B.the the C.the a D.a the
答案 C 为什么选 C？
2．Identifying similar words，linguists have ______what they call an Indo-European parent language, spoken until 3500 to2000 B.C.
A. made up for B.brought back to C.got down to D.come up with
答案D 句子是什么意思？？各选项都是什么意思？为什么选D？？
3．NASA’s Mars program was set back when the two spacecrafts failed up reaching Mars, one _____ up in the planet’s atmosphere and the other ____after a software failure.
A. burned,disappeared B.to burn ,disappearing C. burning, disappearing D.burning, disappeared
答案C 为什么？？
4.Immediately I heard the terrible news, my mind went ____,not knowing what to do.
A. empty B.blank C.empty and white D.hollow
答案B为什么？
5．---Are you a visitor here ?
---That’s right. I ____ round the world and now my dream of coming to china ___true.
答案am traveling has come
第二个空为什么用完成时表达？？