grading an answer

i have  a dilemma in terms of the quiz ability in storyline

i have a quiz question and want to assign grading to them and at the same time all questions are correct

let's say it has 2 answers

both are correct

yes    i want to give a grade 100

no      i want to give a grade  0

if i go to insert a quiz- pick many..it can give me grades , however both answers will give the same grade ,i would like each answer to have a different grade 

i see the box besides correct.  How can i give the value of 0 for no

if i went to the quiz pick one- it has the box to give a value for each answer.. however if i choose this quiz, then only one answer can be correct..not both

am stuck