Which (if any) of the following would have a fairly constant rate of change? Explain your answer.

1. The speed of a car as it enters an on-ramp to a freeway until it reaches the freeway speed limit.

2. The rise in temperature of an oven going from room temperature to $350°$.

3. The number of kilowatt-hours of electricity used by one household from 7:00 AM to 10:00 AM.