Please choose the correct answer to the question: A bus traveled 280 kilometers between two cities. It left the first city at 3:00 p.m. and arrived at the second city at 7:00 p.m. What was the average speed of the bus during the trip?

Answer1: 4 km/h Answer2: 40 km/h Answer3: 70 km/h Answer4: 280 km/h

Answer format: answer1/answer2/answer3/answer4