You are presented with the question "What is the distinguishing feature of monotremes?" and the following answer choices: 
- They lay eggs
 - the eyes
 - Veins and arteries.
 - eardrum
 - four limbs
 - layers of fat
 - They have thick fur
 - fur and fat

Now knowing that platypus females lay their eggs in a burrow and examples of monotremes are the Platypus and Echidna, choose the best answer.


 

 They lay eggs        