Which symbol is used to label a male that expresses a sex-linked disorder on a pedigree?

black solid colored square box

Explanation:

A sex-linked disorder of male on a pedigree is expressed by a black solid colored square box.

While a  male that is just the carrier of sex-linked disorder is represented by by a square box whose half part is solid black in color while the other part is colorless.

A colorless square box in a pedigree signifies a male that is neither affected by any trait associated with sex linked disorder nor even is a carrier of any trait/disorder.

the answer is c) an oak tree