there is my another question. let's assume now is 6 p.m and Mary mom just got into home, can I say "Mary has finished her homework when her mom got home"? Because in my thought, "has finished" means Mary finished her homework somewhere between her after school and 6 p.m.No. "Has finished" doesn't make sense in that sentence. The past perfect, "had finished", does: Mary had (already) finished her homework when I got home. Mary had finished her homework by the time I got home.