What is the most important reason to control the conditions of an experiment

Alberta is a 20 year old who has been a vegetarian for 3 years. she comes to you for advice after reading some material online by the meat promoters of america organization. one of their statements is: ". . vegetarians are at risk for protein deficiency because they cannot consume all of the essential amino acids necessary for healthy individuals." how should alberta be advised? she should consume dairy and egg products at every meal to protect herself against protein deficiency she should avoid the "limiting" amino acids because they are limiting her ability to maintain proper protein status because the statement is basically true, she should consider eating small quantities of meat every day in order to avoid protein deficiency although many foods don't provide all the essential amino acids individually, she could consume complementary proteins throughout the day, which would provide all the essential amino acids she needs