Ecological pyramids are a good model to use to show the relationships between trophic levels in an ecosystem because: A: they are exact

B: it shows that the lower levels are needed to support the higher levels

C: it shows that the higher levels do not need any support from the lower levels

D: it shows that the higher levels are bigger than the lower level

B: it shows that the lower levels are needed to support the higher levels.

Explanation: When an ecosystem is healthy, this graph produces a standard ecological pyramid. This is because in order for the ecosystem to sustain itself, there must be more energy at lower trophic levels than there is at higher trophic levels.

as many times as you want

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."