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

空船排水量加上（）等于满载排水量。

A.总载重量

B.净载重量

C.载货量

D.航次储备量