—Morning, madam! What can I do ________ you?

—I'd like a dress for my daughter. [ ]

A. for

B. to

C. with

D. on

一物体A的重力为G，放在粗糙的水平面上，物体与水平面间的动摩擦因数为μ，如图所示，拉力与水平方向的夹角为α，为拉动此物体做匀速直线运动，求拉力F为多大？