Which comma rule does this student need to apply to this passage?

i really thought she loved me but i discovered her grave betrayal one afternoon. it was easy to figure out because she accidentally sent a text to me that was meant for him. i was confused by the text because it said, "don't tell mike." i felt insulted that she thought she could get away with this infidelity. at first i felt very angry but then i felt so hopeless and depressed.

a. use a comma to separate three or more items in series .
b. use a comma and a conjunction to separate two complete thoughts .
c. use a comma to set off a phase or clause at the beginning of a sentence
d. use a comma to separate a coordinate adjective.

Dogs make wonderful pets because they keep us happy and healthy, the topic sentence is "dogs make wonderful pets". can someone me write a unrelated sentences to the topic and can be eliminated. need asap

Read the excerpt from part 3 of the call of the wild. but it was in giving the law and making his mates live up to it, that buck excelled. dave and sol-leks did not mind the change in leadership. it was none of their business. their business was to toil, and toil mightily, in the traces. so long as that were not interfered with, they did not care what happened. billee, the good-natured, could lead for all they cared, so long as he kept order. the rest of the team, however, had grown unruly during the last days of spitz, and their surprise was great now that buck proceeded to lick them into shape. what theme is most supported by the ideas in this excerpt? good leaders are strong and intelligent. loyalty can be a very powerful force. only the strong survive in the wilderness. we are all ruled by our natural instincts.

This passage from chapter 4 of story of my life is an example of which story of plot