Q: How many amino acids are present in proteins, and how many of these are considered essential amino acids?

Answer: (C) 20 amino acids; 9 are essential
Explanation: Proteins are composed of 20 different amino acids. Out of these, 9 amino acids are considered essential, meaning they cannot be synthesized by the human body and must be obtained through the diet. The correct answer is therefore 20 amino acids in total, with 9 being essentials.