Correct option (d) release of fertilisin
Explanation
Ovum secretes a chemical substance, called fertilisin which has number of spermophilic sites on its surface where the sperm of species specific type can be bound by their antifertilisin site. This fertilisin-antifertilisin reaction triggers acrosome reaction The main aim of this reaction is to thin out the number of sperms to reduce the chances of polyspermy.