Perhaps you should try some spelling variations:
viet sach » viet anh, dien sach, viet tech
hieu viet » sieu viet, hieu viec, lieu viet
sach nuoc » sach duoc, cac nuoc, bach tuoc
xanh doi » xanh di, thanh doi, tinh doi
vu sach » vu bach, su sach, vu khach
sach ky » sac ky, sach y, sach ty
nang ma » tang ma, sang ma, mang may
va xanh » va danh, va hanh, va anh
cua tre » cuu tre, cua triet, dua tren
cua te » cua tu

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

• Performing a fuzzy search may retrieve terms with similar spellings: vu sach ky ((nang ma) or (nang cao)) hoi. hieu viet sach nuoc va xanh doi ((cua tre) OR (cua te))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: vu sach ky ((nang ma) OR (nang cao)) hoi. hieu viet sach nuoc va xanh doi ((cua tre) OR (cua te)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "vu sach ky ((nang ma) or (nang cao)) hoi. hieu viet sach nuoc va xanh doi ((cua tre) OR (cua te))".
• Adding a wildcard symbol may retrieve word variants: vu sach ky ((nang ma) or (nang cao)) hoi. hieu viet sach nuoc va xanh doi ((cua tre) OR (cua te))*.