Why is bias sometimes difficult for readers to detect? a. because it's an opinion that looks like a fact b. because it's wordy and tough to understand c. because it's filled with scientific terminology d. because it's not part of the topic

Bias is characterized by an author stating something as if it is unarguably true, when it is actually not-so-clear cut, and the author simply made some assumptions or had some experiences that supported one particular side of the argument. This is in choice A.

Choices B and C may be true but are not defining characteristics of bias, while Choice D is an entirely different fallacy altogether.