Which of the following factors can affect the effectiveness of fumigation?

The effectiveness of fumigation is significantly influenced by various environmental and physical factors related to the conditions of the fumigation process. The correct answer identifies crucial elements such as temperature, humidity, gas concentration, and exposure time. These factors work together to determine how well the fumigant penetrates the materials being treated and how effectively it can eradicate pests.

For instance, higher temperatures can facilitate faster chemical reactions and enhance the efficacy of the fumigant, while optimal humidity levels can improve the absorption of the gas by the target pest. Gas concentration is vital because insufficient levels may not effectively control the pest population, and exposure time is critical, as the pests must be exposed to the fumigant for a set duration to ensure they are fully eradicated.

Cost, the presence of sunlight, and the type of pest are relevant considerations in a broader context of fumigation practices, but they do not directly affect the immediate effectiveness of the fumigation process itself. Therefore, while these other factors might influence operational decisions or planning, they don't compare to the direct impact that temperature, humidity, gas concentration, and exposure time have on the success of fumigation efforts.