"bias" really just means someone's prejudice in regards to an event or idea, whether it's positive or negative.
"they have a particular motivation or agenda" -- this could be correct. people often dramatize stories to get more of a reaction; for example, kids tattling on their siblings tend to play up their emotions so that their sibling gets in trouble for something. that's a motivation.
"they want to tell the story" -- not quite sure what this choice means
"they want to be popular" -- this could be true, if it's a case where telling a story more dramatically would make people like them more. wanting to be popular IS a motivation, which which is what choice 1 states; wanting to be popular is just a more specific choice
"they have a desire to make money" -- this one doesn't really tie into the question. yes, sure, someone might be twisting a story to persuade someone to offer them money, but wanting money IS a motivation, which still leads us back to choice 1.
i would mark the answer as "they have a particular motivation" because that's usually the driving force behind strong bias. people want to convince you to feel a certain way. money and popularity are two examples of motivations, but they don't answer the question as well because they're too specific, in my opinion. choice 1 is general, applying to many cases of bias in story telling, while choices 3 and 4 are more narrow.
