To find the elevation of base camp, we start with Helene's initial elevation of 27 feet above sea level and then subtract the 32 feet she descends.
Starting elevation: 27 feet above sea level
Descent: 32 feet
Calculation:
27 - 32 = -5 feet
This means that base camp is 5 feet below sea level.
So, the correct response is: 5 feet below sea level.