The pH scale measures how acidic or basic a substance is. Normal drinking water needs to have a pH of less than 6.5. Model the normal range of pH values or water, using a compound inequality.

a. 6.5 < x < 8.5
b. 6.5 > x > 8.5
c. 6.5 <(with a line under) x <(with a line under) 8.5
d. 6.5 >(with a line under) x >(with a line under) 8.5