Agroup of veterinary researchers plan a study to estimate the average number of enteroliths in horses suffering from them. the number of enteroliths is determined by surgery or ultrasound. this requires the participation of a radiologist and a surgeon in the study. the researchers decide that they should only enroll horses seen at the best veterinary hospital in the country to ensure correct counts. such a hospital will typically see the most severe cases. the researchers will enroll the first 100 horses seen beginning on the day the study is funded. the resulting interval is likely biased because:
a. the best veterinary hospital is likely to see the most severe cases with larger number of enteroliths.
b. the first 100 horses seen is not an srs of all horses with enteroliths and therefore never representative.
c. a sample of 100 horses is too small to obtain an unbiased estimate.
d. all of the above.