The problem of a limiting amino acid is most simply overcome by

By combining vegetarian protein sources you can ensure that you are getting all 9 amino acids.

Explanation:

Giving up meat creates you to not get all your limited amino acids. This causes incomplete proteins and key amino acids from a diet. These amino  limiting amino acids  are: lysine, threonine, methionine, and tryptophan. Limiting amino acids are found in the shortest supply from incomplete proteins. Incomplete proteins are those found in plant food sources and geletin.

then that particular organisms become extinct.

it's not c. i took the quiz and got it wrong. so my best guess is b.

have a great day, and hope this .