Perhaps you should try some spelling variations:
viet sach » viet anh, dien sach
xanh di » danh di, vanh dai, xanh tai
va xanh » va danh, va hanh, va anh
vu sach » vu bach, su sach, vu khach
nang ma » tang ma, sang ma, mang may
cua tre » cua te, cuu tre, cua triet
di cua » dai cua, doi cua, de cua

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