A scientist plans to find out the cause of decrease in bird population in a location. He interviews 50 people who work in the local oil mine and 45 of them believe that the mine does not affect the birds. The scientist concludes that 90 percent of people in the location believe that the local oil mine does not cause decrease in bird population. Why is the scientist's conclusion most likely unreliable? (2 points) Group of answer choices

a. the results of the investigation cannot be repeated

b. the source of information could be biased

c. bird population cannot be measured accurately

d. the investigation is done by only one person