题干
—I feel tired and sleepy.
—Why not stop ______ for a while?
—Why not stop ______ for a while?
A：rest
B：to rest
C：resting
D：rested
答案(点此获取答案解析）
B
也为F的拉力作用；丙中弹簧的左端拴一小
物块，物块在光滑的桌面上滑动；丁中的弹簧左端拴一小物块，物块在有摩擦的桌面上滑动．用l1，l2，l3，l4依次表示四个弹簧的伸长量，则有( )