John and his best friend Henry were going to take a test. ...............and the teacher never noticed, why did he fail?

Question

John and his best friend Henry were going to take a test. On the night before the test, John studied all night, while Henry, on the other hand, didn't. Henry decided to just copy off of John's test. The next day, the teacher handed out the tests, and John immediately started to work. Henry carefully wrote down the same answers as John. Luckily for him, the teacher never noticed. A week later, the teacher handed the tests back to the class. John got every question right, and received an A. Henry got an F. If Henry correctly copied John's answers, and the teacher never noticed, why did he fail?

Answer 1

Because they got different tests! The teacher eventually noticed Henry was copying when he graded them.

Answer 2

To one of the questions John answered "I do not know the answer." Henry's answer to that question was "I too do not know the answer." That proved Henry was copying John's answers. Hence he got F..

Answer 3

Henry copied the same answer written by John for a personal question. From that the teacher deduced that Henry had copied from John.