Question 19 is based on the passage you have just heard.

Passage Two

听力原文

       (19) My research focus is on what happens to our immune system as we age. So the job of the immune system is to fight infections. It also protects us from viruses and from auto-immune diseases. We know that as we get older, it’s easier for us to get infections, so older adults have more chances of falling ill. This is evidence that our immune system really doesn’t function so well when we age. In most of our work when we’re looking at older adults who’ve got an illness, we always have to have health controls; so we work very closely with a great group of volunteers called “The 1,000 Elders”. These volunteers are all 65 or over but in good health. (20) They come to the University to provide us with blood samples, to be interviewed, and to help us carry out a whole range of research. (21) The real impact of our research is going to be on health in old age. At the moment, we’re living much longer; life expectancy is increasing at two years for every decade. That means an extra five hours a day. I want to make sure that older adults are still able to enjoy their old age and that they’re not spending time in hospital with infections, feeling unwell and being generally weak. (21) We want people to be healthy even when they are old.

19. What is the focus of the speaker’s research?

解析：D。根据录音开头可知，讲话者的研究重点是：随着我们年龄的增长，我们的免疫系统会发生什么变化，故正确答案为D。A项的function在录音中对应job，但根据中心句可知，本文并非在阐释免疫系统的功能，A项错误。而B项利用auto-immune diseases设置干扰，但录音中只是说免疫系统保护身体不受这类疾病侵害，并未说明疾病产生的原因，故排除B项。