Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A): The binding of a sperm causes the cell membrane of the oocyte to become depolarised, which blocks the entry of additional sperms. 

Reason (R): The secretions of the acrosome help the sperm enter the cytoplasm of the ovum through the zona pellucida and the plasma membrane. 

In light of the above statements, choose the most appropriate answer from the options given below.

The binding of a sperm with the plasma membrane of the oocyte causes the depolarisation of the cell membrane of the oocyte. This prevents the entry of additional sperm into the oocyte (fast block to polyspermy). Depolarisation also triggers the intracellular release of Ca²⁺, which triggers cortical reaction resulting in the hardening of the zona pellucida (slow block to polyspermy). The secretions of the acrosome help the sperm enter the cytoplasm of the ovum through the zona pellucida and the plasma membrane. This not the reason why the entry of additional sperm is prevented.