Final answer:
The correct option is a. sanitation. The best control of filth flies is sanitation, which involves removing or eliminating breeding sites. Other control methods include IPM, bait, and screens.
Step-by-step explanation:
The best way to control filth flies is sanitation. Sanitation involves removing or eliminating the breeding sites for flies, such as rotting organic materials or standing water. By properly managing waste and keeping the environment clean, the population of filth flies can be significantly reduced.
Other control methods can be used in combination with sanitation for more effective results. These include IPM (Integrated Pest Management), which combines various strategies to manage pests; bait, which attracts and kills flies; and screens, which physically prevent flies from entering an area.