Fertilization occurs when sperm swim to an egg inside an archegonium.
Each archegonium contains a single egg that is embedded in the prothallus.
Fertilization occurs when sperm swim inside a single egg embedded in the prothallus.
What happens inside the single egg embedded inside the prothallus 
Options:
(1) Earth revolving around the sun
(2) The area was once underwater
(3) gastropod shells
(4) it keeps an organism warm
(5) remains of prehistoric life
(6) fertilization occurs
(7) allow growth
(8) It helps them survive