How many classes are taken in the third year when pag-unawa was taken in the first year?
CREATE TABLE "table1_12148147_2" (
  "subjects" text,
  "first_year" text,
  "second_year" text,
  "third_year" text,
  "fourth_year" text
);
SELECT COUNT("third_year") FROM "table1_12148147_2" WHERE "first_year"='Pag-unawa';