The answer is B. A chemical reaction consists of an endothermic stage (energy taken in to break chemical bonds) followed by an exothermic stage (energy released as bonds are formed). The first stage requires this energy input, which is the activation energy. When the activation energy is reached or exceeded, the reaction will occur. Therefore as soon as this threshold is REACHED, it happens
Well, both tend to feed on already decaying things, so I'd say that the body is at least 20 to 50 days after death. Beetles normally take over around that time because maggots can no longer get through the dry tissue.
A biochemical cycle that is well know to everyone is the water cylce
The flexible barrier that protects the inside is the cell membrane
