The answer is I. 25 meters.
Well if you mean what does the controlled part of a scientific investigation, it is the part of the investigation that will be your control or your base, untouched, original, data and such.
To find the epicenter (the point on the earth's surface where an earthquake begins) during earthquakes, one need to view the seismogram (a record of the ground motion), and at least two other seismographs recorded for the same earthquake. Other instruments such as a map, a compass for sketching circles on the map, a ruler, and a pencil will also be used.
The following are the steps of the triangulation process in the correct order to find the epicenter during earthquakes:
Step 1: Subtract the time of P wave arrival from S wave arrival.
Step 2: See what the time difference is equal to in distance on a seismic wave chart.
Step 3: Draw circles representing the distances from at least three seismograph stations to the epicenter on a map.
Step 4: Find the point where all 3 circles intersect, and you've found the earthquake's epicenter.
