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

"When glaciers melt they leave ridges called moraines. Moraines are unconsolidated debris made up of sediments such as rocks, clay, gravel and sand that have melted from the glacier ice or moved with the glacier as it travels. 
Radon is a natural ground water pollutant often found in well water, igneous rocks and soil. Radon is the natural byproduct of uranium break down. Plumbing in homes have a trap in order to prevent radon from diffusing into the home. Some people must also monitor their basements for radon emissions. 
Tributaries are small  freshwater rivers and streams that flow into larger bodies of freshwater lakes and rivers."