People always seem to associate high prices of products with high quality. But price is not necessarily an indicator of quality. The best teas are often no more expensive than the lower-quality teas. Which one of the following, if true, does most to explain the apparent counterexample described above? ['Packing and advertising triple the price of all teas.', 'Low-quality teas are generally easier to obtain than high quality teas.', 'Most people buy low-quality tea, thus keeping its price up.', 'The price of tea generally does not vary from region to region.']