Perhaps you should try some spelling variations:
xanh doi » xanh di, thanh doi, tinh doi
vat xanh » vat thanh, sat anh, dat anh
doi cua » dai cua, hoi cua
van hac » van hoc, van ha, van hai
van bac » van ban, van bao, dan bac
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
tang ma » mang may, tang van
sang ma » nang ma, sang tao, mang may
cua tre » cua te, cuu tre, cua triet

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ky ((sang ma) OR (tang ma)) hoi. hieu ((van bac) or (van hac)) thuc vat xanh doi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky ((sang ma) OR (tang ma)) hoi. hieu ((van bac) OR (van hac)) thuc vat xanh doi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky ((sang ma) OR (tang ma)) hoi. hieu ((van bac) or (van hac)) thuc vat xanh doi cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky ((sang ma) OR (tang ma)) hoi. hieu ((van bac) or (van hac)) thuc vat xanh doi cua tre*.