You have the US scale wrong. 60% – 69.99% is a D in America and is not considered a passing grade. We barely consider a 70% – 79.99% (C) a passing grade.
80% – 89.99% is a B and 90% – 100% is an A. With hard work and extra credits we can sometimes achieve 101%+ which is an A+ or S.
EDUCATION IN JAPAN COMMUNITY Blog 
You have the US scale wrong. 60% – 69.99% is a D in America and is not considered a passing grade. We barely consider a 70% – 79.99% (C) a passing grade.
80% – 89.99% is a B and 90% – 100% is an A. With hard work and extra credits we can sometimes achieve 101%+ which is an A+ or S.
Dude- this is Japanese, not US.
There was still a US scale.