What should you always pay attention to at the beginning of every lesson?

Source list: 1. you are researching environmentally friendly ways to live. you find a source that has collected data from other sources about how much energy it takes to heat a home with solar power. you try to look at the author's sources from her works cited page, and you can't find any of them. 2. you are researching reasons for legalizing marijuana. you find a source that adds up the amount of money that the government could collect from taxing the drug in the same way they tax alcohol. it was published by mellow gold, a company that sells cannabis seeds. 3. you are researching the pros and cons of music sharing over the internet. you find a government report with an income graph. it shows average incomes for musicians from the sales of their recordings from 1950-1990. 4. you are researching the secret plot behind the john f. kennedy assassination. you find a biography published in 2000 about lee harvey oswald (who was charged with shooting kennedy) by a respected history professor at princeton university. read the above source list. choose one source that is not reliable. give two reasons why this source is not reliable.