Correct Answer: Celebrate

Solution : The third option is the correct answer.

Lament means to complain or express grief. A word that is appropriately opposite in meaning is celebrate, which means to acknowledge a happy day or event with an enjoyable activity.

The meanings of the other options are as follows:

Deplore means to disapprove of something.

Decry means to publicly denounce.

Regret means to repent over one's actions. None of these words serve as antonyms for expressing grief.

Hence, the correct answer is celebrate.