D. Making up the rules for the game.
Some of the reasons can be:
If you're a pre-teen or a teenager who has only started menstruating, you may find that it takes a while for your period to settle in and become regular.
I couldn't think of anything else, but hope this helped enough!
To find the best answer, ask your mom!
~Aurora
The answer is A. The short periods of intense activity are called intervals and it is used in strength building exercises.
