Perhaps you should try some spelling variations:
duoc tren » nuoc tren, thuoc tren, dung tren
dang mau » dong mau, dang van, dang su
van hanh » van thanh, ban hanh, van anh
va hanh » va thanh, va danh, ban hanh
duc tre » duc tien
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
cac tuc » cac toc, cac tu, cac tac
hieu ve » hieu va, hieu van
mau hoa » cau hoa, ma hoa, mai hoa
ky dang » ky nang, ky danh
ve cac » va cac, vien cac

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 dang mau hoa. hieu ve cac tuc ((va hanh) or (van hanh)) may ((duc tre) OR (duoc tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky dang mau hoa. hieu ve cac tuc ((va hanh) OR (van hanh)) may ((duc tre) OR (duoc tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky dang mau hoa. hieu ve cac tuc ((va hanh) or (van hanh)) may ((duc tre) OR (duoc tren))".
• Adding a wildcard symbol may retrieve word variants: tu sach ky dang mau hoa. hieu ve cac tuc ((va hanh) or (van hanh)) may ((duc tre) OR (duoc tren))*.