Final answer:
The first and second drive gears (D1, D2) in an automatic transmission should be used for uphill driving and heavy traffic. They provide more power and torque. They should not be used for highway cruising or downhill driving.
Step-by-step explanation:
On a vehicle with automatic transmission, the first and second drive gears (D1, D2) have specific use cases. The first drive gear (D1) is designed for uphill driving or when driving in heavy traffic where a lower gear ratio is needed for more power and torque. The second drive gear (D2) can be used for moderate uphill driving or when driving in hilly terrain. It provides additional power and control over the vehicle's speed.
Both D1 and D2 gears should not be used for highway cruising or downhill driving as they limit the vehicle's top speed and can cause excessive engine RPMs or braking.