Correct Answer: praise

Solution : The third option is the correct choice .

The noun complaint means a statement that something is unacceptable or not satisfactory.

The noun praise means to express admiration. Thus, it is the antonym for complaint .

The meanings of the other options are as follows:

• Challenge is to question something's accuracy or truth, or to invite someone to take on a difficult task.
• Carp is to complain or find fault with something persistently or in a petty manner.
• Demur is to express hesitation in response to a request, often indicating doubt.

Therefore, the antonym for complaint is praise .