Sure, let me try to help you on this one.
Green color in plants is given off by a pigment called chlorophyll, which is located in the chloroplasts.
As we all know, chloroplasts are responsible for producing energy from sunlight with photosynthesis.
Now, let's eliminate all the wrong answers.
Green plants are responsible for water vapor in the atmosphere - well, that's simply not true. Plants are the one taking water vapor, not the ones to release it.
Green plants use photosynthesis, not cellular respiration - not true. Cellular respiration is still used by plans; however, they make their own food unlike us. (Ah, lucky plants!)
Green plants are primary consumers. Not true. Plans are primary producers, not consumers.
Lastly, green plants are responsible for the oxygen in the atmosphere. That's true, since plants release oxygen through photosynthesis.
Answer: Green plants are responsible for oxygen in the atmosphere.
