Perhaps you should try some spelling variations:
viet cac » vien cac, viet bac, viet cau
sach bai » sach dao, cac bai, sach xa
van sach » ban sach, van hach, ngan sach
tu sach » thu sach, te sach, tu cach
bai cuu » bai cua, bai cung
viet ca » viet ha, viet co, viet a
cuu tre » cua tre, cau tren, cau treo
su sach » so sach, vu sach
lo van » le van, vo van, so van
x hoi » xa hoi, o hoi, x ho

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) or (su sach)) ky nang x hoi. sieu ((viet cac) OR (viet ca)) lo van sach bai cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (su sach)) ky nang x hoi. sieu ((viet cac) OR (viet ca)) lo van sach bai cuu tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (su sach)) ky nang x hoi. sieu ((viet cac) OR (viet ca)) lo van sach bai cuu tre*".