None of them is true; the explanation is here:
- F: They can be still active at the same time, since the cat can alternate between sleeping and being awake, both each hour; meaning at night, it's possible that hamster and cat be active simultaneously.
- G: Same explanation with F, just that it is day that cat can do be active.
- H: The hamster and dog have different times when they wake up, so two of them are active, along with the cat.
- J: Only two of them can be active.
- K: There are exactly two animals that can be active; night and day.