Mrs. Gilbert is interested in determining how many students spend 4 or more hours doing homework each week. She asks every student who earned Honor Roll for the first semester. Is her survey biased or unbiased?

A. biased, because she didn't ask random students
B. unbiased, because she asked every student on honor roll
C. biased, because she only asked students on honor roll
D. unbiased, because first semester is over