During that time, Mr. Li was wondering why she dropped chemistry and ____ medicine.

A．took over

B．took out

C．took up

D．took off

通常各国海商法和有关国际公约中所调整的海上救助是指（）。

A.纯救助和无效果无报酬合同救助

B.雇佣救助和以无效果无报酬原则确定救助报酬的救助

C.雇佣救助和纯救助

D.无明确规定