Answer:
D. Broca's area.
Explanation:
Broca's area is the part of the brain which takes care of the expressive parts of the language, both in spoken and written form. What this means is that it controls your ability to speak and write, rather than understand what's being said to your or written.
When Fernando's grandma had a stroke, her Broca's area was damaged because she could understand everything, but she couldn't produce language herself (can't speak properly).