A car's speed, in miles per hour, is recorded over a 20-minute trip. The car starts from rest (0 mph), increases its speed steadily for the first 5 minutes until it reaches 40 mph, maintains a constant speed of 40 mph for the next 10 minutes, and then steadily decreases its speed to 0 mph over the last 5 minutes. Which of the following statements about the car's speed is true?
The car's speed was increasing for 10 minutes.
The car maintained a constant speed for 10 minutes.
The car's speed was decreasing for 10 minutes.
The car reached its maximum speed at 5 minutes and then immediately started decreasing.
