Answer:
3
Explanation:
The picture is depicting the process of photosynthesis. The equation for photosynthesis is:
→
Here, and are carbon dioxide and water and they're reactants - inputs. and are glucose and oxygen and they're products - outputs.
In the picture, there's an arrow going into the leaves, so it must be either carbon dioxide or water. Water is already labelled, however, so it must be carbon dioxide. Eliminate 1, 2, and 4. Already, we can see that the answer is probably 3. But let's just check.
There is another arrow coming out of the leaves. This can be either oxygen or glucose. However, it can't be glucose because glucose, which is sugar, is not released into the atmosphere - the plant needs to use it. So, the output arrow is oxygen.
Thus the answer is 3.
Hope this helps!