Compounds that exist naturally in plants and a plant proect itself from bacteria and disease are called

Explanation:In the root nodules of many legumes, symbiotic nitrogen-fixing bacteria called Rhizobia reside. The relationship between a host legume and the Rhizobia is symbiotic or mutualistic in which both partners get benefit.  Once the Rhizobia have established themselves in the root nodule, the plant provides carbohydrates (food) to the bacteria, and in return the Rhizobia provide ammonia for the formation of amino acids and nucleotides.  

a.  exacerbate the natural greenhouse effect  

Explanation:

Greenhouse effect is a phenomena in which the the diatomic gases like carbon dioxide, carbon monoxide, methane, sulphur dioxide and nitrogen oxides traps the light energy from the sun which is responsible for increasing the global temperatures.

The human activities like burning of the fossil fuels, deforestation, and others can increase the abundance of greenhouse gases in the atmosphere. Therefore, a.  exacerbate the natural greenhouse effect  is the correct option.