[originaltext]　　The average family spends about one sixth of its income on food

　　The average family spends about one sixth of its income on food. Because food is expensive, it is important to spend money wisely when you shop. A careful shopper can prepare nutritious and delicious meals inexpensively. (16) Here are some hints to help you shop better. Buy only the food that you need. There are several ways to avoid buying extra food. First, (17) make a shopping list before you go to the store. Then, when you are at the store, follow your list carefully. Furthermore, do not go shopping if you are hungry. When you are hungry, food looks very delicious and you want to buy more than you need. Finally, go shopping alone if you can. If you shop with young children, they often ask you to buy them unnecessary food like candy. When you have a selection, choose the least expensive brand of a product. There are three points to remember when you buy a can of tomatoes, for example. First, (18) look at the advertisements in the newspaper to see if your supermarket is having a "special" on canned tomatoes. In addition, when you are in the store, you should check the price per pound of tomatoes. Sometimes you save money if you buy the larger-sized can; sometimes, however, you don’t. Third, remember that a grade A product or a more expensive
　　product is not necessarily more healthy than a grade B or less expensive product. Grade A tomatoes may look better.
　　16. What does the speaker mainly talk about?
　　17. What is the suggestion to help shop better?
　　18. Why does the speaker advise to read the advertisements in the newspaper before shopping?