The correct option is D The stamens are joined in a single group.
In the case of hibiscus, the filaments of the anther's are fused to form a single group. Hence, the hibiscus flower is termed monadelphous.
In other cases, stamens may be free or united in different ways. Based on the design of the cohesion of stamens, the androecium are divided as polyandrous, monadelphous, diadelphous, and polyadelphous.