题目

阅读理解 Parents often think that time spent with their kids will gradually decrease in adolescence. But a new study suggests that while teens try to avoid spending a lot of time together with their parents, private parent-child meetings may actually increase in their early adolescent years. And that may raise a teenager's self-esteem (自尊) and social confidence, especially if it is the time that spent with Dad, the researchers added. The researchers created a long-term study in which they invited families in 16 school districts in central Pennsylvania to participate. In each family, a 静止在光滑水平面上的物体，受到一个水平拉力。当力刚开始作用的瞬间，下列说法正确的是（    ） A．物体同时获得速度和加速度           B．物体立即获得加速度，但速度仍为零 C．物体立即获得速度，但加速度仍为零   D．物体的速度和加速度仍为零