The level of oxygen in the air is measured in a garden and on a city road. which location has a higher level of oxygen and why? the oxygen level is the same in both places because oxygen production by photosynthesis remains constant, regardless of location. the oxygen level in the city is higher because the exhaust gases from vehicles produce oxygen through the release of carbon dioxide. the oxygen level in the garden is higher because the plants are constantly releasing oxygen through photosynthesis.

I would say the garden has more oxygen. oxygen and carbon dioxide is completely 2 different elements. and since there are more plants, most likely, if it has enough sunlight, the garden will have a better oxygen, because for plant photosynthesis it releases oxygen as their by product.
however please note that if the garden is dark, no light, the garden will lower the oxygen concentration because plants respire and they release carbon dioxide instead. photosynthesis only occurs in light condition as its the source of energy.

The correct answer is  b)