In case of bad weather

Photosynthesis produces organic matter, and respiration decomposes it. When the organic matter produced by photosynthesis is greater than that decomposed by respiration, the organic matter in plants will accumulate and the starch in the organic matter will be converted into soluble sugar. Photosynthesis and respiration of plants are related to temperature. In rainy weather, the photosynthesis of plants is weak, and less organic matter is produced, while plants can breathe and consume organic matter, so reducing the greenhouse temperature and maintaining the temperature difference between day and night can inhibit the respiration of plants.

So choose B.