在交通运输中，受自然条件影响最小的是

A．航空

B．海运

C．铁路

D．公路

Annie Jump Cannon, ________ discovered so many stars that she was called "the census taker of the sky".

A．a leading astronomer,

B．who, as a leading astronomer,

C．was a leading astronomer,

D．a leading astronomer who