Laura’s total utility from consuming 8, 9, and 10 bonbons is 35, 42, and 45, respectively. Her marginal utility from the 9th bonbon is

Laura’s total utility from consuming 8, 9, and 10 bonbons is 35, 42, and 45, respectively. Her marginal utility from the 9th bonbon is
A.7.
B.4.67.
C.42.
D.77.
正确答案：7.