Fact 1: An egg requires warmth to survive.

Fact 2: Inside of the eggs, the embryos grow by shedding their inelastic shell or exoskeleton.

Given the two facts above, answer the question "What inside of a shell requires warmth to survive?" with the following options: 
- oysters
 - abalone
 - bullfrogs
 - sand
 - beads
 - water
 - embryos
 - Echinoids


 

       embryos  