I’m very sure it would be carbon dioxide, plants use carbon as part of photosynthesis, glucose is there food, oxygen is their afterproduct. So the answer is carbon dioxide
The answer is option B "declining number and variety of the species in an area." Biodiversity is a variety of life for example a ecosystem has many species which makes it a biodiversity. Now a loss of a biodiversity would be loosing a huge amount of species in that area or ecosystem which would mean the answer is option B.
Hope this helps.
Tropical rainforests biome are typically hot and wet.