Anyone wanna write a short expository paragraph about why turtles have shells?

Turtles have shells evolved from ribs.  Turtles and other animals with shells use their shells like shields to protect themselves from predators, or animals that hunt them. Turtles needed a shield on their backs and stomachs because they faced predators in the ocean from both above and below.

i would say that these are the two thesis statements best for a literary analysis essay on recurring themes in shakespeare's romeo and juliet:

1.  in romeo and juliet, shakespeare demonstrates that love comes in a variety of forms, be it romantic, familial, or between friends.

2.  shakespeare explores the struggle for identity through the character of juliet in his play romeo and juliet.

the other theses aren't reoccurring in this play. 

explanation:

uhh i would say.. 100 years or innovation?