Fact 1: Fertilization occurs when a sperm and an egg fuse to form a diploid zygote.

Fact 2: Male gametes are called sperm.

Given the two facts above, answer the question "Fertilization occurs when an egg and what join together to form a diploid zygote?" with the following options: 
- rapid expansion
 - testosterone
 - gastropod shells
 - penis
 - peachleaf willow
 - pollen
 - male hormone
 - male gamete


 

        male gamete 