The child merits serious attention at this age.

Answer: Option B

Demands : an insistent and peremptory request, made as of right.
Deserves : do something or have or show qualities worthy of (a reaction which rewards or punishes as appropriate).
Suits : a set of outer clothes made of the same fabric and designed to be worn together, typically consisting of a jacket and trousers or a jacket and skirt.
Invites : make a polite, formal, or friendly request to (someone) to go somewhere or to do something.
Merits : the quality of being particularly good or worthy, especially so as to deserve praise or reward.

Synonym of Merits is Deserves