单选题 .  In August, environmentalists in the Philippines vandalized (肆意破坏) a field of Golden Rice, an experimental grain whose genes had been modified. Its seeds will be handed out free to farmers. The aim is to improve the health of children in poor countries by reducing vitamin A deficiency, which contributes to hundreds of thousands of premature deaths and cases of blindness each year.
    Environmentalists claim that these sorts of actions are justified because genetically modified crops pose health risks. Now the main ground for those claims has crumbled. Last year a paper which was published in a respected journal found that unusual rates of tumours and deaths in rats that had been fed upon a variety of genetic modification (GM) (转基因) corn. Other studies found no such effects. But this one enabled campaigners to make a health-and-safety argument against GM crops—one persuasive enough to influence governments. After the study appeared, Russia suspended imports of the grain in question. Kenya banned all GM crops. And the French prime minister said that if the results were confirmed he would press for a Europe-wide ban on the GM corn.
    There is now no serious scientific evidence that GM crops do any harm to the health of human beings. There is plenty of evidence, though, that they benefit the health of the planet. One of the biggest challenges facing mankind is to feed the 9 billion-10 billion people who will be alive and richer in 2050. This will require doubling food production on roughly the same area of land, using less water and fewer chemicals. It will also mean making food crops more resistant to the droughts and floods that seem likely if climate change is as bad as scientists fear.
    If the Green revolution had never happened, and yields had stayed at 1960 levels, the world could not produce its current food output even if it ploughed up every last acre of cultivable land. In contrast, GM crops boost yields, protecting wild habitat from the plough. They are more resistant to the vagaries of climate change, and to diseases and pests, reducing the need for agrochemicals. Genetic research holds out the possibility of breakthroughs that could vastly increase the productivity of farming.
    Vandalizing GM field trials is a bit like the campaign of some religious leaders to prevent smallpox inoculations: it causes misery, even death, in the name of unscientific belief.1.  The phrase "contributes to" (Para. 1) probably means ______.