The text talks about the predisposition of children to laugh, this behavior is affected when they are accompanied by adults since they control their impulse to laugh before the humour moment or even at the funniest moment because they consider it indecent. According to the above, the word unseemly refers to an inappropriate attitude (children laughing) for a specific situation (moments before the fun or even the most fun moment with adults). So the correct answer is D. Improper
