The author's argument about paranoia is presented primarily by:
presenting the diagnosis and suggesting means for protection.
Option (a) is too vague. It does not provide the answer clearly. The author refers to paranoia as a mental aberration only in the acute case; hence this will not be applicable in general. There is no experiment being conducted. Option (b) is ruled out. Option (c) is out of scope. Option (d) captures the author’s argument perfectly.