This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
All the following are sulphur containing amino acids found in proteins except 
Select and explain. 
A. Cysteine, B. Cystine, C. Methionine, D. Threonine
D: Threonine
Answer: D: Threonine 
Explanation: Sulfur-containing amino acids: Cysteine, Methionine.
Reference: Vasudevan 7th  ed, pg 24