The correct option is A. Unisexual flowers contain either male reproductive organs (stamens) or female reproductive organs (pistil/carpel), but not both. Plants with unisexual flowers can be monoecious (male and female flowers on the same plant, e.g., maize, cucumber) or dioecious (male and female flowers on separate plants, e.g., papaya, date palm). Papaya is a dioecious plant, having separate male and female trees with unisexual flowers. Hibiscus, Mustard, and Sunflower typically have bisexual flowers, containing both stamens and pistil/carpel within the same flower.