Perhaps you should try some spelling variations:
thanh cau » thanh chau, thanh mau, nhanh cau
sach thi » sach thu, sach tai, sach thieu
nam thuc » nam thuoc, am thuc, nam thu
thuc van » thuc vat, thuc dan, thuc va
su triet » su tien, ve triet
tu sach » thu sach, su sach, te sach
qua nam » quan nam, cua nam, quang nam
van han » van hanh, van phan, van nhan
han tai » hang tai, nhan tai, van tai
su viet » so viet

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach thi thanh cau hoi. hieu qua nam thuc van han tai ((su triet) OR (su viet))~".
• Adding a wildcard symbol may retrieve word variants: tu sach thi thanh cau hoi. hieu qua nam thuc van han tai ((su triet) OR (su viet))*.