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.
Initial elevation: 27 feet above sea level
Descent: 32 feet
So, we calculate:
27 feet - 32 feet = -5 feet
This means base camp is 5 feet below sea level.
Thus, the correct response is:
5 feet below sea level.