Don't wander from the subject.

不要离题.

《简明英汉词典》

Be careful not to wander from the subject.

注意不要离开正题.

辞典例句

Don't wander from the subject: stick to the point , ie Don't digress.

不要离题, 要针对这一问题谈.

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You might wander from the subject if you don't pay close attention.

如果你不认真的话,会离题的.

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Do not wander from the subject.

不要离开正题.

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