What potential sources of bias are present, if any? select all that apply. a. certain grids may have been much more severely damaged than others. the grids that are selected may not be representative in terms of damage. b. the sample only consists of grids that are easy to get. these grids may not be representative of the population. c. certain grids may have been much more severely damaged than others. severely damaged grids may have fewer occupied households. d. there are no potential sources of bias.