题目

Green sea turtle Strange，but the green sea turtle is not that green．  It’s certainly not as green as a tree．  In fact，its shell(壳)is nearly black or brown．The largest hard-shelled sea turtle is between 200 and 300 pounds heavy and a shell is between 36 and 43 inches(英尺)long．But its head is smaller than other turtles． Little baby green sea turtles are only two inches long．As the turtle grows up，its shell keeps mostly black while the body turns orange or brown．Young turtles like living in the sea，especially in areas with 1ots of sea grasses． Green sea t下列关于摩擦力和弹力的说法正确的是A.摩擦力的大小总是跟正压力的大小成正比B.静止的物体一定受到静摩擦力的作用C.滑动摩擦力总是阻碍物体间的相对运动D.物体受到弹力作用时就一定受到摩擦力的作用