A family drove their car to a vacation destination. The graph above shows the amount of gas in the car's gas tank vs. the miles that they traveled. Which of the following statements must be true based on the given graph?(No Calculator)
The family started their trip with a full tank of gas.
The family stopped to get more gas on $3$ different occasions.
The family's car used gas at a relatively constant rate per mile throughout the entire trip.
The family's car did not use gas at a relatively constant rate per mile throughout the entire trip.