When was the start of the construction of the unit that's been in commercial operation since 04.03.1987?
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 "construction_start" FROM "reactors" WHERE "commercial_operation"='04.03.1987';