The best hope for ending the COVID19 pandemic is a vaccine. There is no shortage of candidates. The World Health Organization is tracking 34 in various stages of development. How well they will work though,is another matter. On September 9th Astra Zeneca, a drug firm, announced it was pausing its trials after a participant fell ill. Such pauses are common in vaccine development, a discipline in which effort does not always bring reward. In 1987 the first trial of an HIV vaccine began in Maryland. Three decades later, the cupboard remains bare.
The news about COVID-19 in two new papers is more encouraging. The first written by a team of scientists at deCODE genetics,an Icelandic company,and published in the New England Journal of Medicine,reports antibody levels in 1，200 Icelanders who had been infected with the SARS-CoV-2 virus and recovered. More than 90% tested positive for antibodies twice - once immediately post infected and again four months later. People who had suffered more serious disease,such as those who had been hospitalized,developed higher levels of antibodies. So did men and older people, both of whom are at greater risk of more severe illness.
The four-month lifespan is cheering for two reasons. Antibodies that hang around are more likely to offer immunity. That means a vaccine that provokes （驱使；刺激） their production should provide reasonably long-lasting protection. They are also easier to find.
In the second study, scientists led by Tao Dong,an immunologist at the Medical Research Council（MRC），in Britain, went hunting for T-cells. These get less press than antibodies, but play an equally vital role in battling infections and securing long-term protection. Their importance is vividly demonstrated by HIV，which targets and kills them.
Al Edwards, an immunologist turned biochemical engineer at the University of Reading who was not involved with either paper, is cautiously optimistic. The immune response to the disease seems to be working roughly as expected, he says. If that continues,then vaccines developed to trigger long-lasting immunity should work at least in theory.
  In practice,it is still too early to celebrate. Dr. Edwards warns that immunology has never been a predictive science. There is no test that can show definitively that a vaccine will work short of actually trying it in the real world.



What can we infer from the first paragraph？ ______

A. Scientists have made great achievements in HIV vaccine.
B. The vaccine is the only way of ending the COVID-19 pandemic.
C. The COVID-19 is bound to be developed by a drug firm in no time.
D. While many people work on the vaccine, it is hard to develop a vaccine successfully.

Which of the following statements is most probably a logical judgement to the passage？ ______

A. Antibodies that hang around can offer immunity.
B. A vaccine will not work short of actually trying it in the real world.
C. The higher levels of antibodies are, the more serious disease people will suffer.
D. T-cells are less important than antibodies in battling infections and securing protections.

What does the underlined word "them" refer to in paragraph 4？ ______

A. T-cells
B. HIV
C. Antibodies
D. Long-term protection

What is Al Edwards' attitude towards he vaccine？ ______

A. Negative
B. Indifferent
C. Disapproval
D. Cautious