Final answer:
Keiko's reaction to Henry speaking Japanese is that she starts laughing and says she doesn't speak Japanese.
Step-by-step explanation:
Keiko's reaction to Henry after he speaks Japanese to her is option d. She starts laughing and says she doesn't speak Japanese.
This can be inferred from the fact that she starts laughing and responds by saying she doesn't speak Japanese. This suggests that Keiko is amused by Henry's attempt to speak Japanese and tries to communicate to him that she doesn't understand the language.