When scoring the exam, the score for each of the questions is given only for fully correct answers. This means that the question will be deemed as correctly answered only when the correct answer or all of the correct answers are selected. A single incorrect answer in a multiple-response question invalidates the entire question.
The exam pass/fail grade is independent of the number of correct answers, and is calculated based on the score that's achieved out of 1,000. Each question carries a different number of points since each question is considered to be of a different level of difficulty. This means that even if you were to answer 70% of the questions correctly, you can get scored at 60% or lower if all the questions that were answered correctly carried a lower score. I encourage you to answer all the questions during the exam, as even a few unanswered questions...