Averita, this is the solution:
Step 1: Let's review what are the requirements that an unbiased sample meets:
1. Each member of the population is equally likely to be chosen
2. The sample is representative of the whole population
3. The sample should be large enough to generalize the results.
Step 2: According to the previous definitiion, the survey that would produce an unbiased sample is:
c. A polling company surveys downtown workers to determine how much support there is among city residents for the construction of a new highway that runs downtown.