Final answer:
Man-made dams are built to provide a more reliable water source for human use, and while they offer benefits like flood control and hydroelectric power, they also have significant ecological and social impacts.
Step-by-step explanation:
Among the options provided about man-made dams, the true statement is: d) They are constructed to provide a more dependable water resource for human use. Man-made dams help in controlling floods, generating hydroelectric power, providing irrigation, domestic water supplies, and recreation.
However, the impact of dams on river ecosystems and nearby communities can be significant. For instance, they do affect the character of the dammed river downstream by altering the water temperature, flow, and ecology, which in turn can obstruct fish migration. Additionally, they can lead to the loss of wildlife habitats and require relocating people if the reservoir floods existing lands. Careful planning and management are essential to balance the benefits of dams with environmental and social considerations.