Fact 1: Platypus females lay their eggs in a burrow.

Fact 2: Examples of monotremes are the Platypus and Echidna.

Given the two facts above, answer the question "What is the distinguishing feature of monotremes?" with the following options: 
- They lay eggs
 - the eyes
 - Veins and arteries.
 - eardrum
 - four limbs
 - layers of fat
 - They have thick fur
 - fur and fat


 

 They lay eggs        