Excuse me , can you tell me         ?

A．when does the plane leave

B．how long the plane has left

C．when the plane leaves

D．when did the plane leave

下列运算正确的是

A．m⁴•m²=m⁸

B．（m²）³=m⁵

C．m³÷m²=m

D．3m﹣m=2