This is my answer. How you think about my answer?
Answer: The first and second options are random samples.
First, assign numbers and drawing the number from a bowl would be a great way to get a random sample. Everyone has the same chance of being selected.
Second, using an alphabetical order is just like the first choice. The chances are the same for everyone.
However, in the third choice, you won't get a random sample. You will get an old and young group. Not a random group of the population.
M=21 that should equal -15