Correct choice is (a) Montage
The explanation is: The placement of the electrodes on the cranium in order to take the EEG is the montage. The placement can involve 21 electrodes. In order to ensure the correct placement of the electrodes, a cap with perforations at the correct locations is used. This cap is the cranial cap or the montage cap. When taking the EEG, the sensors or the electrodes are plugged in the respective perforations and the signal is acquired.