The answer is; D
The angle at which the sun rays strike the earth at the equator is more or less 90 degrees while you move towards the poles, it much less than this. This means that the unit of sunlight per surface area received at the equator is higher than that at the poles. This is why the equator is always warmer than the poles.
The immune system and the nervous system maintain extensive communication, including 'hardwiring' of sympathetic and parasympathetic nerves to lymphoid organs. Neurotransmitters such as acetylcholine, norepinephrine, vasoactive intestinal peptide, substance P and histamine modulate immune activity.
The Nucleus is the control center, or brain of the cell.
The first step is to identify the problem. There are factors to consider in keeping a plant or a tree healthy. These include water, oxygen, sunlight, soil, nutrients, climate, and other environmental conditions. If the environment seems to suit the other trees in the garden, ruling out other factors can be useful in determining why only one tree seems to be unhealthy. Once the problem is identified, a scientific investigation must be done to gather data and pieces of evidence which can explain why this event actually occurred. One of the best ways to gather evidence is through observing the tree and checking other signs which might identify if the tree is diseased. Once the gathered data are analyzed and the cause is identified, proceed in thinking of ways on how to solve it. In seeking a solution, it is best to ask information from experts and proper authorities.
Earthworms have no special respiratory organs. Gases are exchanged through the moist skin and capillaries
