1. Only the signal from the two sensors were used
2. Only the signal from the two sensors was used
3. Only the signals from the two sensors were used
You can assume the sensors are two thermometers. The signal is the voltage values to represent the temperature. There were two sensors at two places.
Which one is right?
"There were two sensors at two places" - means there were 2 signals. I assume you maintained 2 readings, and didn't combine the 2 signals in to 1, did you?