What could be the possible cause of low air compressor output?

You selected both answer 1 (Excessive dirt in the intake air filter) and answer 2 (Defective air compressor), which are correct. Low air compressor output can be caused if the air filter is clogged with dirt—this restricts airflow and the compressor cannot work efficiently. A malfunctioning or worn-out compressor itself can also directly result in reduced output. Water in the reservoir tanks does not affect compressor output, so that answer would have been incorrect. To solve similar questions, focus on direct causes affecting the compressor or its input, not unrelated issues downstream.