Fact 1: Cartilage is a tough tissue that contains a protein called collagen.

Fact 2: Collagen contributes to meat toughness.

Given the two facts above, answer the question "What can a certain protein affect in meat?" with the following options: 
- health
 - piousness
 - stamina
 - retina
 - toughness
 - liveliness
 - saltiness
 - Energy


 

     toughness    