Jet fuel is the largest cost for airlines, and the cost of jet fuel for the three major state-owned airlines accounts for about 40% of the total cost. In recent years, with the continuous rise in oil prices, the operating costs of airlines have continued to increase. People in the industry believe that although airlines are facing huge pressure on oil prices, they will not raise ticket prices. Which of the following most strongly supports the views of the industry? ['Many airlines carry out "fuel-saving projects" and use computers to accurately measure aircraft refuelling.', 'Fuel surcharges other than ticket prices have been raised.', 'In order to avoid vicious competition, several large airlines have formed a price alliance.', 'Due to the improvement of the economic situation, the passenger source of the aviation market is increasing.']