Life on earth depends on water, and there is no substitute for it. The current assumption

is that our basic needs for water-whether for drinking, agriculture, industry or the raising of fish-will always have to be met. Given that premise, there are two basic routes we can go: more equitable(平衡的) access to water or more drastic engineering solutions.

Looking at the engineering solution first, a lot of my research concentrates on what happens to wetlands when you build dams in river basins, particularly in Africa. The ecology of such areas is almost entirely driven by the seasonal regime of the river—the pulse of the water. And the fact is that if you build a dam, you generally wreck the downstream ecology. In the past, such problems have been hidden by a lack of information. But in this century, governments will have no excuse for their ignorance.

The engineers' ability to control water flows has created new kinds of unpredictability too. Dams in Africa have meant fewer fish, less grazing and less floodplain(泛滥平原) agriculture, none of which were anticipated. And their average economic life is assumed to be thirty years. Dams don't exist for ever, but what will replace them is not clear.

The challenge for the next decade is to find new means of controlling water. Although GM technology will allow us to breed better dry-land crops, there is no market incentive for companies to develop crops suitable for the micro-climates of the Sahel and elsewhere in Africa. Who is going to pay for research on locally appropriate crops in the Third World？

This brings us to the key issue in any discussion of water: money. To talk about a water crisis covers difficult problems such as poverty. In the next decade every household in Britain will have a water meter, and we will pay for what we use just as we do for gas or electricity. That can be resolved and a similar system will eventually be adopted across Europe and the US. But consider the problems of water supply in Mexico City or Delhi. If you're rich, you drink mineral water and may even have a swimming-pool—yet millions in such cities can't get safe drinking water. There is a coming water crisis which is one for the poor.

The word "premise"(Para. 1) probably means "______".

A．assumption

B．promise

C．need

D．crisis