A:物体所受正压力增大时,它所受的摩擦力一定增大
B:物体受到摩擦力作用时,它一定受到弹力作用
C:只有运动的物体才能受到滑动摩擦力作用
D:具有相对运动的两物体间一定存在滑动摩擦力作用
读图,回答下列问题
—Mary looks hot and shy.
—So _______ you if you had a high fever.
People have the belief ________ factories should produce fewer things from raw materials, ________ the supply is growing smaller and smaller.