Answer:
The answer is a. the spacing effect.
Explanation:
This effect explains that learning is more effective when study sessions are spaced. In other words, you wait a short amount of time before your next practice/study session, and only do it for a few minutes every time.
This has proven to give better results than masssed practice (studying or practicing for a long time, only once). The spacing effect helps encode the information in the long-term memory.
