Keep a smile on your face.

脸上要时常挂着微笑。

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Occasionally indulging will keep a smile on your face well into old age.

偶尔放纵一下可以使老人面部保有笑容。

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Yu said: “As a civil servant, I have to keep a smile on my face at all times.”

但余良德表示：“作为一名公务员，我必须时刻面带笑容。”

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Another trick for the TV camera: keep a slight smile on your face WHILE you are talking.

FORBES: Smile For The Camera -Media Training

The only way around this is to put, and keep, a slight smile on your face whenever you are in front of a TV camera.

FORBES: Smile For The Camera -Media Training

This reminds us of what every service organization and retailer should keep in mind: a smile costs nothing.

FORBES: Why Americans Should Go Postal Over The Postal Service Default