A dicotyledonous plant bears flowers but never produces fruits and seeds. The most probable cause for the above situation is:

Dicotyledonous plant or dioecious plant means the male and female reproductive systems occur on separate plants. And both plants produce flowers.

- The unisexual male flower is staminate, which means it bear stamens only. In this fertilization is not possible at all. Hence in this case fruits and seeds are not produced.

- The unisexual female flower is pistillate, which means it bear pistils only. In this fertilization is possible with the help of pollinators and fruits and seeds can be produced.

Monoecious plant has both male and female flowers and produces fruits and seeds.

So, a dicotyledonous plant which bears flowers but never produces fruits and seeds. This situation is possible only when the plant is dioecious and bears only staminate flowers.

Therefore, the correct answer is (d).