The correct answer is <u><em>placer mining</em></u>
Hope This helps!!!
D+b i think... I am not sure, but I am pretty sure that that is what it is, because none of the other answers make sense.
To cause a source to be biased means that it is influenced by your opinion or another factor that is not factual. Bias can take away from the credibility because it is not completely true, as a source should be.
