Whether you intentionally or inadvertently use someone else's words and thoughts, the outcome is that another author's ideas emerge as your own. in this sentence, the word inadvertently means:
a. by writing
b. by accident
c. by plagiarizing
d. by summarizing

The answer for this problem would be B. by accident.

Without any access to dictionaries or the internet about what the word means, context clues are very helpful. And in this situation where there are options to choose from, they give you quite a hand in choosing the right answer. Context clues are the other words in the statement or group of statements that help you with the difficult word. In this problem, the difficult word inadvertently is partnered with the word intentionally by using the conjunction or. Or is used usually when pairing two opposite words. For a much better understanding, the opposite word for intentionally would be unintentionally. Then looking up at the choices, the closest one to unintentionally would be accident.