C. The passage begins with a description of plastic's problems in order to call attention to the good qualities of aluminum.
Throughout the passage the author speaks of plastic in negative terms. He says that it's "not very strong...not very durable...does not decompose." These are all the problems with using plastic as a material for containers. The author then goes on to speak about aluminum. We know that the author favors aluminum because he speaks of all it's positive traits. He says that it is "much stronger...conducts electricity...is very easy to recycle." All of these lines show us that the author pays attention to the good qualities of aluminum.
