Essential amino acids — From the list below, which option correctly identifies essential amino acids for humans?

Introduction / Context:
Essential amino acids cannot be synthesized de novo by humans and must be obtained from dietary sources. Their adequate intake is crucial for growth, repair, and nitrogen balance, especially in children, pregnancy, and illness.

Given Data / Assumptions:

• Candidates: tryptophan, methionine, lysine.
• We apply the standard human essential amino-acid list.
• No special clinical exceptions are invoked.

Concept / Approach:
The essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine (with histidine especially important in growing individuals). Tryptophan, methionine, and lysine are all on this list.

Step-by-Step Solution:

Verification / Alternative check:
Nutrition references and WHO/FAO guidelines agree on these three as essential, with defined daily intake recommendations based on age and physiological state.

Why Other Options Are Wrong:

• Any single choice omits the other essential residues listed; the comprehensive answer is all three.

Common Pitfalls:
Confusing conditional essentiality (e.g., tyrosine when phenylalanine is deficient) with absolute essentiality; misremembering sulfur metabolism and methionine/cysteine interchangeability limits.

Final Answer:
All of these