He has a delicate constitution.

Answer: Option C

Delicate : easily broken or damaged; fragile.
Fit : of a suitable quality, standard, or type to meet the required purpose.
Ungainly : (of a person or movement) awkward; clumsy.
Strong : powerful and difficult to resist or defeat.
Rugged : (of ground or terrain) having a broken, rocky, and uneven surface.

Antonym of Delicate is Strong