循环水控制系统中，“液位1”、“液位2”和“液位3”分别用来表示、、和水池的液位高度，数据类型为型。

A．.the melody of the verse
B．.the melody of the chorus
C．.the rhythm, which is usually on the backbeat
D．.a line that is very catchy, and repeated over several times, so it is easy to remember