听力原文:Ever since the Apollo moon landings, the idea of human expeditions to the Mars has come up repeatedly as the kind of grand adventures that would give focus, purpose, and inspirational lift to the space program. But confronted with the cost—estimated at $150 billion last week—presidents starting with Richard Nixon and others have flinched and resorted to halfway measures tike the shuttle. Why have the Americans developed space shuttle according to the passage?
A.
It is a first step to explore outer space.
B.
It is a follow-up action of the Apollo moon landings.
C.
It is a compromise to the exorbitant human expeditions to the Mars.
D.
It is a compensation for the wishful thinking of human landing on the Mars.