Dear Jenny,

    Now we are in the hospital of our city . My mother and I have a bad cold . We sees many children here . Some people have a cold. Some people have a headache. Some people have a fever. They a re waiting outside the doctor's room .Now it's our turn.

Yours,

Jack

已知甲、乙两行星的半径之比为a，它们各自对应的第一宇宙速度之比为b，则下列结论正确的是（   ）

说说南非是如何利用本地的自然条件来发展经济的。从中你可以得出什么结论？