|std_str_cmp_list is described at
(it's an older version that has been replaced by a call to str_cmp, which in
turn calls one of the new Parser evaluators)
It's purpose as you use it above is to create answer checkers for 3 problems, the answer
to the first problem being a, to the second b and so forth.
It sounds like you would like an answer checker that accepts a or b or c as an answer.
I think what you want is pc_evaluator
# Wrapper for multiple answer evaluators, it takes a list of the following as inputs
# [answer_evaluator, partial credit factor, comment]
# it applies evaluators from the list until it hits one with positive credit,
# weights it by the partial credit factor, and throws in its comment
Something like this might work
ANS( pc_evaluator( [ str_cmp('a'),1,'first possible correct answer'],
[ str_cmp('b'),1,'second possible correct answer'],
[ str_cmp('c'),10,'best possible correct answer'],
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