亲爱的张先生：
我外出几天之后于今天上午回到办公室，见到你们为庆祝“十•一”发出的邀请，为此我向您表示感谢。
我本能够接受邀请，但不巧我同几个外国朋友事先约好会见，他们正好那天到达，以致不能如愿以偿。
这次希望你们见谅，深信以后有机会见面、结识您和您的同事们。

A．geometry
B．physics
C．violin
D．polytechnic

A．After they finish school, people must learn to be suitable to the many major changes that affect their lives.
B．Parents need to understand the best ways to educate children.
C．People need to understand how certain experiences change their behaviors.
D．Employees make use of the principles of learning to influence the behavior of employers.