Pollen-pistil interaction is a dynamic process involving

A. The pistil has the ability to recognize the pollen, whether it is self or non-self.
B. The pollen grain germinates on the stigma to produce a pollen tube through one of the germ pores. The contents of the pollen grain move into the pollen tube. The pollen tube grows through the tissues of the stigma and style and reaches the ovary.
C. Pollen tube, after reaching the ovary, enters the ovule through the micropyle and then enters one of the synergids through the filiform apparatus.
D. All the events from the pollen deposition on the stigma until pollen tubes enter the ovule are known as pollen pistil interaction. It is a dynamic process involving the above.
So, the correct option is 'All of the above'.