Source- beginning of a river
mouth-end of a river
estuary- area there a river meet the sea or the ocean
tributary-river/stream that flows into another stream, river, or lake
The answer would be D. One of the main reasons for Antarctica's dryness is its lack of precipitation.
From an archived question I looked up for you, I believe it should be water-table aquifers. By the way, if you look in the link above, replace the 4449929 with 482974 to see the answer to it!
1 and 2 A. 3 is C. 4 is B