In the process of maintaining OSN equipment, I often see fans running at full speed, and the equipment reports TEMP_OVER alarms. The common causes and handling methods are?

In the process of maintaining OSN equipment, I often see fans running at full speed, and the equipment reports TEMP_OVER alarms. The common causes and handling methods are?
A . The dust filter is very dusty, which affects the ventilation, and the dust filter needs to be removed for cleaning
B . The dust inside the fan is serious, which affects the speed, and the fan needs to be removed to clean it.
C . The power module of the single board has serious dust accumulation, which affects heat dissipation and needs to be removed by pulling out the board
D . The cooling function of the optical module is abnormal, and the optical board needs to be replaced

Answer: A