To find the elevation of base camp, we start with the hiker's initial elevation and subtract the amount she descends.
Starting elevation: 33 feet above sea level Descent: 46 feet
We calculate the new elevation as follows:
\[ \text{New elevation} = \text{Starting elevation} - \text{Descent} \] \[ \text{New elevation} = 33 - 46 = -13 \text{ feet} \]
Since -13 feet indicates a location below sea level, this means base camp is at 13 feet below sea level.
Thus, the correct answer is d. 13 feet below sea level.