That was a dauntless action!

The correct answer is A.

Dauntless means fearless or brave. It is the opposite of cowardly.

Devious means crafty or cunning. It is the opposite of honest.

Irresolute means indecisive or hesitant. It is the opposite of decisive.

Secretive means keeping things secret or private. It is the opposite of open.

In the sentence “That was a dauntless action!”, the speaker is praising the person who took the action for being brave. The other options do not fit the context of the sentence.