@Brian_BH Could you share the rationale for the other tagged QIDs outside of 403446?
QID 404109:
Wrong question.
QID 400365:
Question asks specifically about an amino acids in which a thiol group is modified, and the correct answer is cysteine and its sulfur group. Requiring familiarity with the structure of cysteine and its containing a sulfur thiol group specifically.
QID 401879:
Wrong amino acid, my bad (again, I think the search function got me). I’ll be more careful moving forward. 
QID 403446:
Question specifically requires knowing that cysteine is both polar, and typically uncharged at physiological pH, as an important discriminator to eliminate other answer options that are either nonpolar, or polar and charged.
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