A low pitch sound example would be like a crocodile. They can produce sound so low for the human ear to hear. Thunder can also produce exceptionally low pitched sounds that are felt much as they are heard.
The first and second at first glance looks to have a misplaced modifier, but the first one is the correct answer. :)
The answer to the question is a. Packed.
Also along the lines of global warming you could talk about environmental problems like using cleaner energy like solar panels and why we don't use more of them in places with more sun exposure like deserts that could give us more power
