Process of spermatozoon head penetration into oocyte is seen in histologic specimen. What is the name of this process?

Process of spermatozoon head penetration into oocyte is seen in histologic specimen. What is the name of this process?

1.  Denudation


2.  Acrosomal reaction


3.  Cortical reaction


4.  Chemotaxis с


5.  *Penetration