What U15 3rd Quad has a U15 2nd Quad of ACGS?
CREATE TABLE "winning_head_of_the_river_championship_e" (
  "crew" real,
  "open_1st_viii" text,
  "open_2nd_viii" text,
  "open_3rd_viii" text,
  "u16_1st_viii" text,
  "u16_2nd_viii" text,
  "u16_3rd_viii" text,
  "u15_1st_quad" text,
  "u15_2nd_quad" text,
  "u15_3rd_quad" text,
  "u15_4th_quad" text,
  "u15_5th_quad" text,
  "u15_6th_quad" text
);
SELECT "u15_3rd_quad" FROM "winning_head_of_the_river_championship_e" WHERE "u15_2nd_quad"='acgs';