Perhaps you should try some spelling variations:
thieu nien » thien nhien
hieu vien » hieu hien, hieu viec, hieu tieng
doanh van » doan van, doanh va, doanh ban
va doanh » van doanh, vay doanh, va danh
van cua » vang cua, ban cua, dan cua
cua tre » cua te, cuu tre, cua triet
sach ky » sac ky, sach y, sach ty
nang ma » tang ma, sang ma, nang cao
sach tu » sach thu, cach tu, sach ty
ma hoi » mai hoi, xa hoi, ma hoa
da do » dao do, da dot, dau do
do va » do van, so va

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

• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ky) OR (sach tu)) nang ma hoi. ((hieu vien) OR (thieu nien)) da do va doanh van cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach ky) or (sach tu)) nang ma hoi. ((hieu vien) OR (thieu nien)) da do va doanh van cua tre~".
• Adding a wildcard symbol may retrieve word variants: tu ((sach ky) or (sach tu)) nang ma hoi. ((hieu vien) OR (thieu nien)) da do va doanh van cua tre*.