Courses that are more challenging than regular high school courses are known as:

A. technical courses.

B. extra credit courses.

C. rigorous coursework.

D. extensive coursework.

I believe the answer is: rigorous coursework.

rigorous coursework refers to the type of coursework which difficulties far surpassed the average requirement expected from each topic, but all questions should be based on the things that exist within the curriculum.

This type of coursework is usually used in selection process to enter prestigious universities.

Rigorous coursework - apex