Recall the definition

Essential amino acids are those amino acids that the human body cannot synthesize in sufficient amount and therefore must be obtained from the diet.

Check each option

• A: Alanine
  Alanine is a non-essential amino acid.

• B: Valine
  Valine is an essential amino acid.

• C: Aspartic acid
  Aspartic acid is a non-essential amino acid.

• D: Serine
  Serine is a non-essential amino acid.

Conclusion

The only essential amino acid among the given options is: $\boxed{\text{Valine}}$

Comparison with stored correct answer

Stored correct answer = B
Derived answer = B

Hence, the derived answer agrees with the stored correct answer.