None of our early ancestors could digest milk as adults because their bodies never had to—milk drinking simply wasn't an option. As people began to extract milk from animals, though, some people developed the ability to keep drinking it throughout their lives.
Scientists now know of a milk-related mutation (变异）in our genes—the chemical instructions for life that we carry in almost every cell in our bodies. People who have a mutated form of one particular gene can drink milk just fine. People without the mutation tend to get sick from milk.
To figure out where, and possibly why, milk drinking started, some scientists have been looking at who has the milk-digesting mutation today. Patterns are striking.
Most adults in Northern and Central Europe are able to digest milk—and they do. Cheese and butter and other dairy products are popular in countries such as Sweden, Denmark, Germany and England. Because European settlers dominated North America, most people here can handle milk just fine, as well. That may explain why ice cream is such a popular dessert in the United States.
In much of Africa, Asia and South America, on the other hand, people tend to avoid dairy products because they lead to diarrhea(腹泻)and other stomach problems (That's why you won't typically find cheese on the menu at a Chinese, Japanese or Ethiopian restaurant. ). Native Americans are also unable to digest milk.
Based on these genetic patterns, scientists have long thought that milk drinking started in Northern Europe, where dairy is an institution and the milk-digesting mutation is everywhere.
A recent study painted a different picture. With a computer medal, Thomas and colleagues looked at the spread of the milk-drinking mutation, farming and other related factors. Working back-ward, the scientists concluded that the first milk-drinkers lived in Central Europe around what's now Hungary about 7，500 years ago. The practice didn't start farther north, as scientists had thought be-fore.
Which of the following is the proper order of events according to the passage?
a. Their children were able to digest milk as adults.
b. They got sick from the milk.
c. Some people got a mutation in their genes.
d. Some people tried drinking milk from animals.
e. Some people started to drink milk from animals on a regular basis.

A．c→d→b→e→a	B．d→e→b→c→a
C．d→b→e→c→a	D．e→d→b→c→a

Most people in the USA can digest milk because __________

A．they have strong stomachs

B．their ancestors were Europeans

C．that's where milk drinking started

D．farmers raise a lot of cows there

Which of the following is LEAST likely to appear on the menu in a Japanese restaurant?

A．Butter.

B．Vinegar.

C．Fish.

D．Beef.

Which of the followings is the author most likely to agree with?

A．Milk drinking first started in Northern Europe.

B．Milk drinking first started in Central Europe.

C．North American Indians were able to digest milk.

D．Dairy products are very popular in North Korea.

The main focus of the scientists' research was __________.

A．mutation of human genes

B．development of the human stomach

C．why milk drinking started

D．where milk drinking first started