The correct option is C strong
The word 'delicate' refers to being fragile and sensitive.
Option A, fit refers to being of the right shape and size.
Option B, ungainly refers to being clumsy or awkward.
Option C, strong refers to being able to withstand force and pressure.
Option D, rugged refers to having attractively strong and rough-hewn features.
Thus, according to the meaning, the word 'strong' is the opposite of the word 'delicate'.