不定项选择 B2B (Business-to-business) loyalty programs reward businesses for their purchase of goods and services from suppliers.

单项选择题 ‏春天是放风筝的好季节。当风筝在空气中向上飞行时，下列说法正确的是：​

判断题 固体材料在外力作用下的变形，在外力卸去后不能消失的变形称为塑性变形。（  ）