"Choosing the Best Answer"

Multiple choice tests often implement a "choose the best answer" policy. This can be very frustrating for the test-taker. The ability to choose the best answer is not always the same thing as choosing the right answer. What is the value in choosing the best answer out of a few not-so-great answers? This may teach students some problem-solving techniques, such as how to choose the best possible solution to a problem where there is no perfect solution, but it does not accurately assess a student's knowledge of a subject. For example, when I was in sixth grade, I had to take a nutrition class. One of our test questions was:
Which of the following should one eat? a)a healthy meal b) a healthy diet.
My teacher argued that the best answer was "a healthy diet" because one healthy meal wont do much for you in the long run, unlike a healthy diet, which is more beneficial. However, this question confused me as an eleven-year-old because you can't eat a healthy diet without eating healthy meals. Eating a healthy diet includes eating healthy meals. Maybe there was a best answer, but both answers were right. Sometimes neither answer is right, even if there is a "best" answer. These kinds of questions seem unnecessarily tricky and confusing.