Sam drove 96 miles in 90 minutes. His average speed during the first 30 minutes was 60 \mathrm{mph} (miles per hour), and his average speed during the second 30 minutes was 65 \mathrm{mph}. What was his average speed, in mph, during the last 30 minutes?

**Answer Choices**

A. 64

B. 65

C. 66

D. 67

E. 68