Final answer:
The subject is 'Tu hermano' and the correct answer is C. cierra.
Step-by-step explanation:
The subject of this sentence is 'Tu hermano' which means 'Your brother' in English. The verb used with 'Tu hermano' is 'cierra' which means 'closes' in English. So, the correct answer is C. cierra.
Example: Tu hermano cierra la ventana porque siempre tiene frío. (Your brother closes the window because he is always cold.)
Learn more about Spanish Verbs