(B) Hibiscus and mustard
Bisexual flowers contain both stamens and pistil. Hibiscus and mustard are bisexual, while papaya and watermelon are unisexual.
The passage explicitly states: "the flower may be unisexual (papaya, watermelon)… or bisexual (Hibiscus, mustard)." Any option containing papaya or watermelon is incorrect. Only option (B) lists two bisexual flowers.