If you're a junk food lover, you will know this：No matter where you shop or what brand you buy, when you tear（open a bag of potato chips, it's almost always half filled. This can be quite disappointing. I always hope those bags are quite full. But there's actually a god reason for this--and no, the food companies are not pulling a fast one on you.
In the manufacturing industry. “slack fill” is the empty space that's placed around a product on purpose. The idea is that the extra room can "protect" your Lays or Tostitos（brands of chips）. The trip from the production machine to the market can be grille long and hard！If it weren't for "slack fill', your chips would probably look more like breadcrumbs（面包屑）.
But wait, there's more, Think that the bag of potato chips was filled up with air？It actually is nitrogen gas(氮气). Chips manufacturers fill bags with this gas to help kelp chips fresh If it were filled with regular air, the chips would likely turn wet and soft in 1994, scientists found that exposing chips to nitrogen not only heaped to prolong the shelf life（保质期）, but also made them stay crisp（脆的）What's more, nitrogen is a natural gas and completely harmless.
Still feel you are tricked by the empty bag？There's a way to tell the amount of potato chips in your snick bug before you break it open. In 1966, the Fair Packaging and Labeling Act was passed. which requires manufacturers to show the net weight of their products' contents. When shopping for your next bag of potato chips, pay attention to the net weight that's printed on the bag. This way you'll be able to know if it is worth your money.
33．What does the underlined phrase in Paragraph 1 mean?
A．Doing a test. B．Playing a trick.
C．Changing its focus. D．Reaching an agreement.
34．What do we know about “slack fill”?
A．It makes the chips’ bag look empty. B．It can shorten the products' trip.
C．It is only used or Lays or Tostitos. D．It can prevent damage to the chips
35．Why do chips' manufacturers choose nitrogen to fill up the bag?
A．To keep chips tasting good. B．To make chips look good.
C．To reduce the products cost. D．To avoid causing harm to humans.
36．What are we advised to do in the last paragraph?
A．Value a product by its net weight. B．Work out the products net weight.
C．Notice the products' shelf life. D．Pay more attention to the empty bag.

33．B  34．D  35．A  36．A