3. When glaciers melt, they leave ridges of rock, gravel, sand, and clay called _______.
A. moraines
B. cirques
C. drumlins
D. eskers
4. Which gas is a source of natural groundwater pollution?
A. Radon
B. Carbon
C. Oxygen
D. Hydrogen
17. What are tributaries?
A. Rivers that flow into other streams
B. Ocean currents that flow into other oceans
C. Rivers that flow into lakes
D. Streams that flow into oceans