热定形
参考答案：
利用合成纤维的热塑性，在热能和张力的作用下，使产品形态稳定的加工过程
Chinese exports have been hit hard by falling world demand, with millions of workers _______ to their villages after the factories that employed them closed down.
A．returned
B．returning
C．have returned
D．return
如图所示，用绳子拴住一个苹果并悬挂起来，把苹果拉近自己的鼻子静止，松手后，苹果将向前摆去，接着又反向摆回来，你原地不动，苹果会打到你的鼻子吗？为什么？
