An economic theory states that there is an "inverted U-shape" relationship between economic growth and environmental quality, that is, deterioration first, then improvement. At the beginning, with the economic growth, residents' income continued to increase and the environment began to deteriorate; When the economy has grown to a certain level, the quality of the environment has begun to reverse and continues to improve. If the following information is true, can you verify whether this theory is true? ["A's economy is developed, and its country's environmental quality has undergone a process from deterioration to gradual recovery.", 'B is a traditional agricultural country. In recent years, due to the use of mechanical operations, the national economy has developed rapidly, but the natural environment has not changed significantly.', 'In order to ensure sustainable development, the government of country C has decided that it is better to reduce the national economic growth rate than to damage the natural environment.', 'Due to the deterioration of the international economic situation, in recent years, the national income of country D has been declining, but the quality of the environment has not improved.']