eliminate 1,2 because deforestation can't never increase oxygen and decrease soil erosion. deforestation is an activity due to excessive cutting of trees that may lead to decrease in biodiversity in the area and increase in the absorption of carbon dioxide.
the best answer for this is number 4, it can increase the absorption of carbon dioxide in the earth athmosphere, plants naturally absorb carbon dioxide and give off oxygen gas in the process of photosynthesis.