In The late 1990s, flight attendants around the word noticed a dramatic
increase in "air rage". This is the official term for what happens when someone becomes extremely angry or upset on a plane. These people may become dangerously violent that the plane has to land somewhere and unload the passengers. Air rage may be the result of several factors. The general worsening of travel conditions in recent year has led to crowded planes and frequent delays. At the same time, airline have generally reduced the amount of seat space for each passenger, so people are more likely to feel stressed and aggressive. One other factor, however, has nothing to do with the airline industry. Flight attendants say that very often the people who become violent on planes have had too much alcohol to drink, either before the flight or in the plane.
What is the meaning of the words "crowded plane" in line 4?
1. not too many passengers
2. plane for the king
3. plane for the prince
4. too many passenger