这张优惠券到月底前都有效。

This coupon is ___valid until the end of the month.

教授的推理非常严谨，他的观点很有说服力。

The professor's reasoning was very ___valid, and his points were convincing.

这张优惠券在月底前有效。

This coupon is ___valid until the end of the month.

你的担忧是有根据的，因为确实存在风险。

Your concerns are ___valid because there is indeed a risk.