The World Health Organization reports a number of people have died of the Ebola virus in central Africa during the last few months. Ebola, also known as Ebola hemorrhagic (出血) fever or Ebola viral disease, is a rare and deadly illness with high death rates in humans and primates. The natural source of Ebola virus remains unknown, although bats seem to be the most likely source.
The Ebola virus began spreading after victims were discovered in northeastern Gabon. So far, it is the third time Ebola has spread through Gabon since 1994. Health officials believe people moving across the border spread the disease from Gabon to Congo. Ebola is highly infectious and kills up to 80% of its victims. Researchers do not know the method with which the virus first appears in humans, but they believe it is through infected animals. The disease then spreads from person to person through blood and other body liquids.
Ebola victims treated early have the base chance of survival. Signs of Ebola include a high temperature, diarrhea, muscle pains and bleeding inside the body, in severe cases, victims experience chest pains and death. There is no known cure for the disease and no way yet to prevent it.
Scientists at the American National institutes of Health are working to develop a vaccine(疫苗) to prevent Ebola. Doctor Cary Nobel is leading the research effort at N-l-H testing center in the eastern state of Maryland. He says that during the past two years, the vaccine has been tested on small animals and monkeys for safety and effectiveness.
In the most recent study, four monkeys who had been given the vaccine were completely protected from a deadly injection of the Ebola virus. The study was described in November in Nature magazine. Doctor Nobel says the tests appear to have moved scientists one step closer to a vaccine for humans.
Where does the Ebola virus come from?

A．Bats.

B．Monkeys.

C．Infected humans.

D．Something unknown.

When infected with Ebola virus, people may experience the following except ____.
A. heart attack                    B. a rise in temperature
C. chest pains                     D  bleeding inside the body
What can we learn from the passage?

A．Once infected with the Ebola virus, people can never survive.

B．Half of the Ebola victims will lose their lives.

C．No cure has been found for the disease.

D．Scientists have succeeded in preventing Ebola.

What is Doctor Nobel's attitude towards the tests?

A．Discouraged.

B．Positive.

C．Doubtful.

D．Not mentioned.