If you are writing matching questions or true/false questions or other questions where guessing might be effective, you might want to use an alternative grader. The default grader gives partial credit for the part that are correct, and gives the student correct/incorrect for each part.
There is another grader that doesn't give partial credit and doesn't tell which which parts are correct until they are all correct. Perhaps that will do what you want?
To use it, add
install_problem_grader(~~@std_problem_grader);
See if that does what you want.
Davide