连续时间信号与通常所说的模拟信号的关系为（）

A.完全不同

B.是同一个概念

C.不完全相同

D.无法回答

The main idea of this passage is that ______.

A．light causes sea color

B．sea coloration is varied because of a combination of length of light waves and micro- scopic plant life and silt

C．microscopic plant life causes sea color

D．water composition causes sea color