Astudent examines a cell under the microscope and determines that it is a eukaryote. all but one structure could the student come to this conclusion. which structure is of no ?

The eukaryotes are the organisms that contain the genetic material (DNA) inside the membrane enclosed nucleus. These organisms contain membrane bound cell organelles, such as mitochondria, Golgi apparatus etc. as opposed to the prokaryotic organisms  that contain no membrane bound organelles and no nucleus. The presence of enclosed nucleus and membrane bound organelles helps in determining that the cell is Eukaryote, but the presence of cell wall will be of no help as both the prokaryotes as well as eukaryotes contain cell wall.

Hence, the correct answer is 'cell wall'.

it's c. (to reduce the greenhouse effect/carbon gasses)

"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."