To determine Helene's elevation at base camp, we start with her initial elevation of 33 feet above sea level and subtract the 46 feet she descends during her hike.
Starting elevation: 33 feet Descent: 46 feet
Calculation: 33 feet - 46 feet = -13 feet
This means she is 13 feet below sea level. Therefore, the appropriate response is:
13 feet below sea level