Which of the following is an arithmetic sequence? a. –20, –25, –30, –35, –45, b. 7.2, 3.6, 1.8, 0.9, 0.45, c. 3.1, 6.2, 12.4, 24.8, 49.6, d. –15.6, –12.9, –10.2, –7.5, –4.8,