For 20 consecutive years the pass rate in the national advanced-level exams has increased. The exam questions have not become easier but the students find it easier to obtain top grades now that marks are awarded for course and project work and only 20% of the marks are reserved for the final exams. Last year 130,000 girls obtained two A grades whereas 20 years ago only 34,000 obtained these marks. Before 1987, grades were norm-rated against previous years, with only the top 10% of candidates being awarded an A grade. Since that date no limit to the number of A grades has been set and anyone who scores over 60% receives an A grade. This change has seen the number of A grades awarded more than double.

Question: Girls have been mainly responsible for the rise in the number of A grades.
Options:
A. true, B. false, C. uncertain
Answer: "C"