—Don't forget to phone me when you get to New York.Just let me know you've arrived safely.

—I won't forget.Goodbye then.

—________.[ ]

A. With pleasure  

B. Have a nice trip

C. Don't mention it  

D. It's very nice of you

只在两端受相同外扭矩的钢杆和铝杆，长度和直径也分别相同，则有结论（）。

A．钢杆的最大切应力比铝杆的最大切应力大

B．钢杆的最大切应力比铝杆的最大切应力小

C．钢杆的最大扭转角比铝杆的最大扭转角大

D．钢杆的最大扭转角比铝杆的最大扭转角小