If the stopping distance and average length of a vehicle are 18 m and 6 m respectively, then the theoretical maxi¬mum capacity of a traffic lane at a speed of 10 m/sec is A. 1500 vehicles per hour B. 2000 vehicles per hour C. 2500 vehicles per hour D. 3000 vehicles per hour

The correct answer is $\boxed{\text{B}}$.

The theoretical maximum capacity of a traffic lane is the maximum number of vehicles that can pass a given point on a road in a given amount of time. It is calculated by dividing the length of the lane by the average time it takes a vehicle to travel through the lane.

The average time it takes a vehicle to travel through a lane is equal to the distance traveled divided by the speed. In this case, the distance traveled is equal to the length of the lane plus the stopping distance plus the average length of a vehicle. The speed is equal to 10 m/sec.

Therefore, the theoretical maximum capacity of a traffic lane is:

$$\frac{18 \text{ m} + 10 \text{ m} + 6 \text{ m}}{10 \text{ m/sec}} = 20 \text{ vehicles/sec} = 2000 \text{ vehicles/hour}$$