4、Water stress ________________.

A、
A、can be controlled in an environmentally- and politically-friendly way through the use of aqueducts;
B、
B、is only a concern in arid areas where there is a constant lack of water;
C、
C、will not be a concern by 2025 if the present level of water continues to be used throughout the world;
D、
D、is predicted to be a problem for an increasing percentage of the world's population