How many different values of total power are there for the unit whose construction started on 01.03.1977 and whose commercial operation started on 01.02.1984?
CREATE TABLE "reactors" (
  "unit" text,
  "type" text,
  "net_power" text,
  "total_power" text,
  "construction_start" text,
  "construction_finish" text,
  "commercial_operation" text,
  "shut_down" text
);
SELECT COUNT("total_power") FROM "reactors" WHERE "construction_start"='01.03.1977' AND "commercial_operation"='01.02.1984';