Text 2 The threat of diseases such as influenza or tuberculosis re-emerging in virulent form has been a common theme in recent years. That threat is not limited to human diseases. Our food plants get sick too, and just as human diseases evolve to evade antibiotics, so the diseases that strike our crops evolve to sidestep the resistance genes we have bred into them. For the vast majority of the calories the world eats, the key crop is grain. A ruinous wheat disease we have not had to worry about since the 1950s is making a comeback, and unless we are very lucky, we will not have sufficient defences to protect crops everywhere in the world against it in time. That stem rust would evolve and return to plague us was inevitable, but our lack of preparation to ward it off was not. Research into stem rust was bound to tail off once the disease seemed beaten, but the world let down its guard too far, for ideological reasons. In the 1980s governments of industrialized countries, especially the UK and US, started to lose patience with the "multilateral" agencies that engineered much of the global progress in agriculture after the Second World War. Each government wanted the agencies to dance only to its tune. This included the Consultative Group for International Agricultural Research, the global network of labs that created the "Green Revolution". The CGIAR remains the leading, sometimes only source of agricultural research devoted to global good rather than private profit. "Multilateral" funding meant these labs received income from rich donors with no strings attached. Researchers at the labs were able to spend the money the way they thought best—including the unglamorous task of making sure that crops’ disease resistance kept pace with the diseases. However, for more than two decades, donors have been cutting this funding in favour of only financing projects allied to their own interests. As wheat stem rust re-emerged in 1999, the main CGIAR wheat lab was entering a major funding crisis, and ended up sacking a quarter of its scientists. It has taken until now to beg enough money to fight the disease. There are now signs that donors may be moving back to more open-ended funding, which is to be encouraged. They should also increase their derisory funding for this vital research: stem rust is poised to teach us the dangers of complacency. The world population is predicted to rise by another 3 billion by 2050, yet increases in food production have stagnated, technological fixes are spent, and global warming—and the return of diseases like stem rust—look likely to take back many of the gains we have made. Food security affects political security, and one of the first regions to suffer from stem rust will be the volatile Middle East, including Iraq. Agricultural research for the public good is the only way to provide that security. It is certainly cheaper than building armies. The human and crop diseases once under control have come back again because（）

A. antibiotics do not work anymore.
B. human diseases spread to plants.
C. there is genetic resistance in them.
D. human interventions no longer work.