质量为5kg的物体静止在水平桌面上，当施加在该物体上的水平推力增加到20N时开始滑动，接着以18N的水平推力可维持物体在水平桌面匀速直线运动，该物体受到的最大静摩擦力为______，物体与桌面的动摩擦力因数______；当水平推力为15N而物体仍运动时，物体受到的摩擦力为______；当水平推力为15N而物体静止时，物体受到的摩擦力为______；当水平推力为40N时，物体受到的摩擦力又为______．

Gasoline tanks should be filled（）.

A.to the top to expel all vapors from the tanks

B.to the top so the operator is certain how much fuel he has aboard

C.with only sufficient fuel for the planned trip so excess gasoline is not carried

D.to near the top with some space allowed for gasoline expansion