题目内容：

It’s not every day that United States history mixes with microbes (微生物) in the soil. But when the grassland on the National Mall in Washington, D.C. was replaced, it offered scientists the opportunity to study changes in the soil beneath.

The work focused on the bacteria present in the soil. To the researchers’ surprise, the communities of microbes did not change a lot before and after the replacement. These communities in the soil are known as the soil microbiome (微生物群).

“My lab is interested in how microbes can move around in the environment , and how they change and adapt as a result of this movement,” explains Jo Anne Crouch, the lead author of the study. “We thought that the new ‘imported ’turf (草皮) from New Jersey would introduce different communities of bacteria to the National Mall. However, we found that they weren’t significantly different.”

Crouch’s work focused on turf grass ，defined as a large area of green grass. It is made up of the grass, its roots, and the soil and microbes found with them.

Think of the soil microbiome as similar to the collection of microbes found in the human body. When the microbes are out of balance , it can make someone sick. Crouch says it’s the same for the soil microbiome. Many of the worst diseases in crops or other environments are linked with changes in the soil microbiome.

Additionally, Crouch says that even though the changes between the soils were small, scientists are also starting to appreciate that sometimes a really important microbe is a rare one. This means it would be hard to observe but could greatly affect how the groups function as a whole. “Agricultural areas and other natural spaces are highly and easily hurt by negative changes,” she says. “Microbiomes offer an almost entirely new opportunity to influence interactions among plants and microbes to improve plant productivity and health. ”

1.Why did the researchers feel surprised when they focused on the bacteria in the soil?

A. More bacteria appeared in the soil.

B. Microbes were replaced obviously.

C. Soil microbiome almost remained stable.

D. The soil microbiomes damaged the environment.

2.By studying the turf grass , what did Crouch and her team find?

A. Microbes grew faster in their own community.

B. Soil microbiomes were different in different places.

C. Turf grass adapted to the environment nearby very soon.

D. Similar communities of bacteria were brought by turf grass.

3.Why did the author mention the microbes in the human body?

A. To indicate the two play a similar role.

B. To prove they are both the causes of diseases.

C. To examine the environments people live in.

D. To analyze the changes of human microbes.

4.What does Crouch mean in the last paragraph?

A. Microbes are still as hard to observe as before.

B. Studies on microbiomes can be beneficial to agriculture.

C. Scientists are still puzzled about the effect of microbiomes.

D. Too many microbiomes in the soil mean no harm to plants.