题干
—What do you see, Kitty?
—_________.
A：I see a duck.
B：I hear a bird.
答案(点此获取答案解析）
A
—What do you see, Kitty?
—_________.
A：I see a duck.
B：I hear a bird.
将一木球靠在轻质弹簧上，压缩后松手，弹簧将木球弹出。已知弹出过程弹簧做了40J的功，周围阻力做了-10J的功，此过程物体的