human brain produce natural opiates, called opioids(鸦片). These can stop pain and make us feel good.

　　Others think that we feel good after eating chocolate because of a chemical called anandamide. This occurs naturally in the brain and seems to give us a feeling of happiness. Normally, our levels of anandamide are very low and our body uses it quickly. But two scientists, Emmanuelle di Tomaso of Harvard University and Daniele Piomelli of the University of California believe that the anandamide in chcocolate raises levels of the chemical in our brain. And other substances in chocolate slow down the speed at which we use it. So, chocolate helps us feel happier for longer! Great!

　　But which chocolate is the best? Well, for a start, there's more anandamide in dark chocolate than milk chocolate. So, you need to buy some dark chocolate. Then, you should follow these five tips from connoisseur chocolate makers Ghirardelli. They say that when choosing chocolate, you need to use all five senses:

　　1.Sight: good chocolate has a shine to it.

　　2.Smell: rub the chocolate with your finger to release the aroma. It should have a deep chocolate smell.

　　3.Sound: when you break a piece of chocolate it should snap crisply, creating a sound similar to that of a thin piece of wood being broken.

　　4.Touch: the chocolate should melt easily in your mouth becoming a thick liquid.

　　5.Taste: good chocolate should not taste too sweet or too bitter.

3. Why does the author mention opioids in Paragraph 2?

A. To prove chocolate contains the same chemicals as opioids.

B. To show the sharp contrast between chocolate and opioids.

C. To suggest that chocolate is as highly addictive as opioids.

D. To help explain the reason why chocolate brings pleasure.

4. The underlined word "it" in Paragraph 3 refers to _______.

A. anand amide B. chocolate C. opiate D. Brain

5. Which of the following best suits "perfect chocolate" according to chocolate makers?

A. Milk chocolate that produces a dull sound when broken.

B. Milk chocolate that has shiny appearance and bitter taste.