Once you________ it, it's a piece of cake! It's nothing to worry about.

A．watch out for

B．get the hang of

C．get rid of

D．get away with

一、二等导线测量中，同时间段经气象改正后的距离值测回互差限差为（）mm。

A．±5

B．±10

C．±15

D．±20