用下列材料做成的实心小方块，放入水中会沉下去的是（  ）。 

     When you're invited to have dinner in a restaurant in a western country, please remember: at table, when the hostess picks up her napkin, you may pick up yours and put it on your legs.

      If a servant passes food around, he will pass the dish to you at your left hand so that you can easily serve yourself with your right hand. Never serve yourself while the dish is on your right; it is the turn of your neighbor on the right. Do not reach across the table or in front of someone to get something that you want to eat. It is not polite. Ask him or her to pass it to you.

     There are things in the middle of the table, such as bread, butter, and candies. You shouldn't take any until the hostess tells the servant to pass them to you.

     Do not leave your seat without saying anything. If you need to leave the table to go to the washroom or do something else, you should say "Excuse me for a moment, please."