例如，幼儿知道当他们哭泣或微笑时，有人会回应他们。

For example, infants learn that when they cry or smile someone responds to them.

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做你认为可以帮助他人感觉良好的事情，例如，打招呼或微笑。

Do what you think might help others feel good, for example, say hello or smile.

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当然，在某些情况下，简单的挥手、点头或微笑可能都是合适的。

Of course, in certain circumstances, a simple wave, nod or smile may be appropriate.

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Then when a stranger approaches or someone else approaches there they'll tend to give more of a greeting smile.

当陌生人或其他人接近时,他们是问候式微笑。

耶鲁公开课 - 心理学导论课程节选

The mouth moves up, particularly if somebody is attacking their record or ridiculing them, and they'll smile and--but it's not a sincere smile.

嘴唇移动，特别当有人攻击他们的记录,或嘲笑他们时，他们会微笑，但不是真诚的微笑。

耶鲁公开课 - 心理学导论课程节选

One group of children was a control group; the second group was taught to think back to experience that make them laugh or smile.

一群小孩组成对照组;,有人教第二组小孩回想,让他们大笑或微笑的经历。

哈佛公开课 - 幸福课课程节选