<span>The most approprate answer is a. water. Although over 70% of the earth's surface is water, only a small percentage is fresh water that is suitable for domestic purposes. The high rate of pollution and the over use of groundwater resources can use water faster than it can be replenished. Some rivers and lakes can become so polluted that they cannot be used for domestic or even agricultural purposes. </span>
Not 100% sure but I think its the Barail Range. This would affect them by the mountain acting almost like a barrier between them. So they didn't have much interaction.
