第 48 至 51 題為題組
Scientists are trying to genetically modify the world in which we live. They are even trying to wipe out diseases via genetic modification. For example, researchers have tried to engineer mosquitoes to kill malaria parasites. The malaria parasite is carried by the female Anopheles mosquito. When transmitted to a human, the parasite travels first to the liver and then on to the bloodstream, where it reproduces and destroys red blood cells. An estimated 250 million people suffer from malaria each year, and about one million die—many of them children. There are currently no effective or approved malaria vaccines.
To “kill” malaria, scientists are genetically modifying a bacterium in mosquitoes so that it releases toxic compounds. These compounds are not harmful to humans or the mosquito itself, but they do kill off the malaria parasite, making the mosquito incapable of infecting humans with malaria.
Despite this achievement, scientists are faced with the challenge of giving the modified mosquitoes a competitive advantage so that they can eventually replace the wild population. Complete blockage of the malaria parasite is very important. If some of the parasites slip through the mechanism, then the next generation will likely become resistant to it. And if that happens, the scientists are back where they started.
Another challenge for scientists is to gain public approval for this genetic modification regarding mosquitoes and malaria control. Environmental activists have raised concerns about the release of genetically engineered organisms without any clear knowledge of their long-term effect on ecosystems and human health. There is still a long way to go before genetic modification techniques are put to use in disease control.
【題組】51. What does “that” in the third paragraph refer to?
(A) Some malaria parasites escaping from the ecosystems.
(B) Malaria parasites becoming immune to the engineered bacterium.
(C) Modified mosquitoes becoming more competitive than the wild ones.
(D) Transmission of malaria being blocked from mosquitoes to humans.