This one has been around for a while but I like it!

Students in an advanced biology class were
                                taking their mid-term test.

                                The last question was, 'Name seven
                                advantages of Mother's Milk,' worth
                                70 points or none at all.

                                One student, in particular, was hard put
                                 to think of seven advantages.
                                He wrote:

                                1.) It is a perfect formula for the child.

                                2) It provides immunity against several
                                    diseases.

                                3.) It is always the right temperature.

                                4.) It is inexpensive.

                                5.) It bonds the child to mother, and vice
                                     versa.

                                6.) It is always available as needed.

                                And then, the student was stuck. Finally,
                                in desperation, just before
                                the bell rang indicating the end of the
                                test, he wrote..

                                7.) It comes in 2 attractive re-usable
                                     containers.

                                He got an A+