Which of the Following Statements Is True About Transcranial Direct

Which of the following statements is true about transcranial direct current stimulation?

A) A very high voltage is administered via four or more electrodes placed on the scalp of an individual.
B) Research indicates that negatively charged stimulation increases memory in general.
C) The technique is usually considered painless and safe.
D) Transcranial electrical stimulation of the frontal lobe during slow wave sleep impairs recall of word pairs among people.