A small dog should be belly-up after eating a handful M＆M’s, at least according to conventional wisdom. But watching “Moose”, a friend’s five-pound Chihuahua, race around a living room after his sweet snack makes one wonder: Is chocolate truly poisonous to dogs?
Dogs and humans have similar tastes. But unlike humans, our companions experience dangerous effects from eating chocolate — it can poison them and in some cases is fatal. Chocolate’s danger to dogs depends on its quality.
Chocolate is processed from the bitter seeds of the cocoa tree, which contain a family of compounds known as methylxanthines（一种衍生物）. This class of substances includes caffeine and the related chemical theobromine(可可碱). Chocolate contains a significant amount of theobromine and smaller amounts of caffeine. These chemicals can cause a dog’s heart to race up to twice its normal rate, and some dogs may run around as if “they drank a gallon of espresso,” according to Hackett.
Dogs are capable of handling some chocolate, but it depends on the animal’s weight and the type of chocolate it eats. Unsweetened baking chocolate contains more than six times as much theobromine as milk chocolate, although amounts vary between cocoa beans as well as different brands of chocolate. Less than four ounces of milk chocolate is potentially fatal for Moose and other small dogs.
Around every confection-centered holiday — Valentine’s Day, Easter and Christmas — at least three or four dogs are hospitalized overnight in the animal medical center at Colorado State. But in 16 years, Hackett has seen just one dog die from chocolate poisoning, and he suspects it may have had an underlying disease that made it more exposed to chocolate’s heart-racing effect.
1. The underlined expression “belly-up” probably means______.
A. dead            B. poisonous                 C. running around  D. having a headache
2. All of the following are true EXCEPT______.
A. chocolate’s danger to dogs depends on its quantity and quality
B. people buy lots of chocolate around Valentine’s Day
C. an ounce of unsweetened baking chocolate is safe for Moose
D. there must be some theobromine or caffeine in espresso
3. What can we learn about Hackett?
A. He is an animal doctor.         B. He is a pet shop owner.
C. He is the owner of Moose       D. He is a doctor in a small hospital.
4. It can be inferred from the passage that Hackett believes that__________.
A. chocolate is truly deadly to dogs 
B. it’s OK to give chocolate to a big dog
C. pets are usually ignored around confection-centered holidays
D. a healthy dog probably could survive a chocolate poisoning
5. The passage is mainly about__________.
A. the poisoning of Moose   
B. the compounds of different chocolates
C. a handful M＆M’s chocolate is poisonous
D. the relation between methylxanthines and chocolate poisoning

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