Peter, as well as his two sisters Sondra and Emily, ____ left-handed.

A．is

B．has

C．are

D．have

三台电机M1、M2、M3，当M1起动时间t₁后M2起动，经过时间t₂后M3起动，停止时M3停止，时间t₃后M2停止，时间t₄后M1停止，
请设计出符合要求的电气控制原理图。