I'll give you a question, please answer with step-by-step reasoning process. They say dogs are a man's best friend, this is because of dog's pack mentality and being what?
Options:
- four legs
- frightening
- found outside
- tail
- faithful

Faithful is remaining loyal and steadfast. They say dogs are a man's best friend, this is because of dog's pack mentality and being faithful.
The answer: faithful.