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1·An old dog will learn no new tricks.

老家伙学不出新名堂。

2·An old dog will learn no new tricks.

老狗学不出新把戏。老顽固不能学新事物。

3·You can't teach an old dog new tricks. (an old dog will learn no new tricks.)

谚老狗学不了新把戏；老年人很难适应新事物。