Because plants go through a cycle(the cycle is seed, seedling, plant, flower and tree.) and it takes time for the plant food, water, and nutrients to go though the plant.
The CNS are lined by ependymal cells. Ependymal cells are epithelial cells that monitor the composition of cerebrospinal fluid (CSF)
The most hazardous to his health is lead poisoning. It is because Aaron is still young and he doesn't know mostly all of the things around him and the things that which is bad and good for him. Considering he is a child, he is likely exposed to materials such as toys and he would not know that some of these toys are contaminated with hazardous materials that could contribute to lead poisoning.
I believe the answer is D
