I think that genetically modified foods should be banned．Here's why．

We have no idea of the real impact they have on our environment．While there's currently no hard proof that environmental damage is being done by genetically modified foods, there are a few worrying and suspect events that may actually be tied to these products．Most important is the sudden loss of huge numbers of bee hives．Bees are necessary to the pollination process for soybeans and many other food crops．It's entirely possible that "the law of unintended consequences" has caused the loss of these extremely important insects．

There's also no real way to prevent cross contamination （交叉污染） between modified crops and natural crops．When neighboring fields are planted with different varieties of computable（可共存的） plants, there is a  virtual guarantee of some cross pollination between the fields．

We have no idea of the real impact they have on human beings．There is already documented evidence that genetically modified foods may be the cause of higher allergy （过敏） rates in children, It's impossible to guess v/hat other effects they may eventually cause．

I suspect that most people have forgotten the serious health scare and complete failure that occurred in 1989 that caused death or health problems for hundreds of people．The product causing the problem was L-tryptophan, an amino acid; Commercially produced L-tryptophan is developed through a bacterial fermentation process．One maker of the supplement developed a genetically modified strain of bacteria which was capable of producing higher quantities of L-tryptophan．

Unfortunately, the process "broke" somewhere along the line with the genetically altered bacteria creating an altered form of the chemical which had devastating effects on people who consumed it．

Since there is no way to predict these kinds or changes, it's both foolish and dangerous to introduce genetically modified products into the food chain.

Finally, there's no need for genetically modified foods．Most companies that produce these products will send out statistics about higher output per acre or plants that are more tolerant to negative conditions．But the truth is that the claims, while at least partially true, are mostly rhetoric．

These companies are really just looking for a way to increase their bottom line profits．They may not actually intend to, damage the ecosystem or create new health problems for people．But in my opinion it's not nice to fool Mother Nature．She may offer up a variety of severe surprises in response．

68．What's the structure of the passage?

69．The sudden loss of bee hives may be due to ___       .

       A．environmental pollution from human beings

       B．genetically modified products

       C．cross-contamination between modified crops

       D．cross pollination between the fields

70．Which of the following words best describes genetically modified foods?

       A．Risky．           B．Deadly.         C．Harmful．                 D．Healthy．

71．Most companies advocate the genetically modified products in order to _     _．

       A．increase their output                    B．solve health problems

       C．earn more money                         D．protect the ecosystem