Help please :( Read the example below and think about the writer's tone.

Running as a form of exercise is easy to do because it does not require any special equipment. You will need good shoes, but you may already have a pair that will work. Besides that, the only other thing you will need is a safe place to run. Often people run in their neighborhood or in a park. Others use a treadmill or run at a track, but any of these options, as long as they are safe, can provide a place to get an excellent workout.

How does the writer establish credibility through her tone?
a) by using a mix of formal and informal language
b) by using colloquialisms and idioms
c) by adhering to the conventions of standard written English
d) by using a variety of sentence types and lengths