Final answer:
The appropriate adjective to fill in the blank is 'bruns', as it agrees with the plural noun 'cheveux' (hair) which is masculine.
Step-by-step explanation:
Elle a les cheveux bruns.
The correct adjective to fill in the blank is bruns because it agrees with the plural noun, cheveux (hair), which is masculine.
Example: J'ai les cheveux bruns (I have brown hair).
Learn more about Adjectives in French