题目内容：

Europe’s deadly outbreak of a rare form of E. coli bacteria (大肠杆菌) has brought new attention to food safety issues. One of the problems when people get sick from food is that the simplest question is often difficult or even impossible to answer. Just what did the people eat that made them sick?
Of course, one way to avoid these medical mysteries is to keep dangerous organisms out of the food supply. This is easier said than done, but scientists keep looking for new ways.
Scientists in the United States have developed an experimental system that uses a high-tech optical scanner. The system is designed to identify the presence of contaminants(致污物) like soil or animal waste on fresh produce. These can be sources of E. coli. E. coli bacteria naturally live in the intestines(肠) of humans and many animals. Most kinds of E. coli are harmless but some can make people sick.
The new scanner can also show damage and imperfections that might make the produce unappealing to shoppers.
Scientists designed the system at a Department of Agriculture research center in Beltsville, Maryland. Moon Kim of the Agricultural Research Service led the team.
MOON KIM: “We were requested, we were asked, to develop a method to detect contamination in produce. So we started with the apple as the model sample.”
The scanner uses a high-speed camera placed over the conveyer belt that moves the produce along. As the apples move along the belt, the scanner captures images of each piece of fruit.
Moon Kim says the team hopes the system will be available before long.
MOON KIM: “We are targeting for development in commercial plants for the next several years.”
The scanner can direct a sorting machine to separate the bad apples from the good ones. The system is currently able to show the surface of only half the apple as it speeds by. The inventers hope to improve the process so it can show the whole surface.
1.What is the main topic of the text?

A．Bacteria.   B．A high-tech scanner.

C．A camera    D．Food safety.

2.E. coli bacteria ______.

A．broke out all over the world              B．comes from soil or animal waste

C．is extremely harmful to health              D．does not cause illness

3.The high-tech scanner ______.

A．can help to sort out different fruits

B．make the produce appeal to shoppers

C．can only capture images of the whole apple

D．can identify the presence of contaminants

4.What can be inferred from the text?

A．The scanner needs to be improved.

B．The scanner will be available in the next several years.

C．Moon Kim is unwilling to develop the scanner.

D．The scanner is connected to a sorting machine.