(1) Taxes can be used to change people's behavior and are often used to reduce the amount of demerit goods people buy. Demerit goods are products which can cause negative effects in an economy. Cigarette smoking is one example and taxing smokers should, in theory, reduce the demand for cigarettes. Taxes are also used to protect the natural environment by charging those who pollute or damage it. For example, countries such as the UK and China tax cars based on the engine size because vehicles with larger engines tend to cause more pollution. (2) Another example is the tax on plastic bags. Before July 2009, Hong Kong used an average of 30 million plastic bags every day! For quite a small population of 7 million people, this meant the average person in Hong Kong was using more than four plastic bags every day, often just using each plastic bag once only. This amazing figure meant that the country's landfills would be unable to cope with the bags when they were thrown away. (3) Hong Kong's introduction of a small tax (6.5 US cents) on the use of plastic bags has encouraged people to use recycled shopping bags. In fact, demand for plastic bags fell by 85 percent within the first 2 days of the tax being introduced. This follows similar moves made by other countries such as China (in 2007) and Ireland in 2002).
What is one important idea related to demerit goods mentioned in Paragraph (1)?