题目内容：

    For almost 500 years, people have wondered what deadly disease wiped out most of the Aztecs (阿芝特克人）. The locals called it cocolizthi, and now a team of scientists think they know exactly what that was. The outbreak is considered to be one of the deadliest epidemics (传染病）in human history. For centuries, its cause has been debated by historians. New evidence suggests that the Aztecs died from a type of bacteria called salmonella enterica.

An international team of scientists came to this conclusion after analysing the skeletons (骨骼) of 29 Aztecs buried in a cocoliztli cemetery in the Oaxaca region of Mexico. The scientists obtained samples from the teeth of ten of the skeletons. They compared these with their database of bacteria and found traces of salmonella enterica.

Salmonella enterica can cause enteric fever, of which typhoid (伤寒）is a type. Today, there are around 21 million cases of typhoid worldwide and it is considered a global threat.

The Aztecs were fierce hunter-gatherers who settled in what is now Mexico at the beginning of the 13th century. From their incredible capital city Tenochtitlan(now Mexico City),the Aztecs fought wars with other tribes until they ruled much of the region.

The Aztecs ended up controlling large parts of Mesoamerica--now much of Mexico and Central America--until Spanish explorers arrived in 1519 and brought with them advanced weapons and deadly diseases. The team believe that the domesticated animals, such as goats and horses, which the explorers brought with them carried the deadly bacteria.

By 1545,not even 30 years after the Spanish had arrived, Mexico's Aztec nation started coming down with a terrible illness. Symptoms included high fever, headaches and bleeding from the eyes, nose and mouth. Within five years, up to 15 million people---more than 80%of the population at the time--had died from the mystery illness they called cocoliztli. The Aztec people had no immunity (免疫) to fight the disease.

“We cannot say with certainty that salmonella enterica was the cause of the cocolizti epidemic,” said Kirsten Bos from the Max Planck Institute for the Science of Human History in Germany.” We do believe that it should be considered a strong candidate."

1.Which helped the scientists come to the conclusion.

A.Certain traces of deadly diseases carried by goats and horses

B.Extensive comparison of Aztecs buried in a cocoliztli cemetery

C.Definite discoveries of infected tooth samples from the database

D.Small amounts of certain bacteria in the teeth of the skeletons

2.Which of the following is TRUE about the Aztecs?

A.They had a population of about 15 million around 1545.

B.Their livelihood depended on raising domesticated animals.

C.Their population dropped sharply in the middle 16th century.

D.They won the wars with the Spanish despite being poorly equipped.

3.The underlined word “it” in the last paragraph refers to_    

A.cocolizti epidemic B.salmonella enterica C.the typhoid D.the Max Planck Institute

4.The passage is mainly about

A.how the Aztecs got infected with salmonella enterica

B.why the Aztecs had no immunity to fight typhoid

C.which reason caused the Aztecs to abandon their native land

D.what led to the military and economic decline of the Aztecs