Answer:
4 letters
Explanation:
When we receive random information that will be later used for a test, our memory focuses on the first few elements, this is called the primacy effect, and then in the last few elements, this is called the recency effect.
These 2 effects increase our chances of remembering the first and the last few elements of a list, but unfortunately, it doesn't happen the same with the elements in the middle, and these tend to get all fuzzy in our minds.
This is called the serial position curve, and that is why the student will most likely remember the first 2 and the last 2 words of the test.