It is not controversial to say that an unhealthy diet causes bad health. Nor are the basic elements of healthy eating disputed. Obesity raises susceptibility to cancer, and Britain is the sixth most obese country on Earth. That is a public health emergency. But naming the problem is the easy part. No one disputes the costs in quality of life and depleted health budgets of an obese population, but the quest for solutions gets diverted by ideological arguments around responsibility and choice. And the water is muddied by lobbying from the industries that profit from consumption of obesity-inducing products.

    Historical precedent suggests that science and politics can overcome resistance from businesses that pollute and poison, but it takes time, and success often starts small. So it is heartening to note that a programme in Leeds has achieved a reduction in childhood obesity, becoming the first UK city to reverse a fattening trend. The best results were among younger children and in more deprived areas. When 28% of English children aged two to 15 are obese, a national shift on the scale achieved by Leeds would lengthen hundreds of thousands of lives. A significant factor in the Leeds experience appears to be a scheme called HENRY, which helps parents reward behaviours that prevent obesity in children.

    Many members of parliament are uncomfortable even with their own government’s anti-obesity strategy, since it involves a “sugar tax” and a ban on the sale of energy drinks to under-16s. Bans and taxes can be blunt instruments, but their harshest critics can rarely suggest better methods. These critics just oppose regulation itself.

    The relationship between poor health and inequality is too pronounced for governments to be passive about large-scale intervention. People living in the most deprived areas are four times more prone to die from avoidable causes than counterparts in more affluent places. As the structural nature of public health problems becomes harder to ignore, the complaint about overprotective government loses potency.

    In fact, the polarised debate over public health interventions should have been abandoned long ago. Government action works when individuals are motivated to respond. Individuals need governments that expand access to good choices. The HENRY programme was delivered in part through children’s centres. Closing such centres and cutting council budgets doesn’t magically increase reserves of individual self-reliance. The function of a well-designed state intervention is not to deprive people of liberty but to build social capacity and infrastructure that helps people take responsibility for their wellbeing. The obesity crisis will not have a solution devised by left or right ideology—but experience indicates that the private sector needs the incentive of regulation before it starts taking public health emergencies seriously.

解析：C。根据题干中的government action和be effective可定位到原文第五段第二句。该句指出，政府的行动在个人受到激励而愿意采取回应时才会发挥作用。C项中的have the incentive对应原文中的are motivated，act accordingly对应原文中的respond，故C项是政府采取的行动见效的条件，为正确答案。

错项排除：A项中的polarised debate在第五段第一句出现，但这里只是说polarised debate早该停止，并不是政府行动见效的条件，故排除。原文第五段最后一句提到了left or right ideology，但这里说的是左翼和右翼都无法提出解决方案，没有提及意识形态的差异得到解决对政府行动的影响，故排除B项。D项中的private sector出现在全文最后一句，原文是说经验表明，需要先制定法规给予激励，才能让私营部门严肃对待公共卫生紧急事件。也就是说要先制定法规，即政府部门采取行动，私营部门才会严肃对待危机，D项内容与题干无关，故错误。