Perhaps you should try some spelling variations:
khanh tai » thanh tai, hanh tai, nhanh thai
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
duc van » duc va, duc manh, duc phan
cuc tre » duc tre, cua tre, cuu tre
co hai » co dai, co hoi, so hai
ve cac » va cac, vien cac
o hai » so hai, o lai, _ hai

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 nang ((o hai) or (co hai)). hieu ve cac ((duc van) OR (duc tan)) khanh tai cuc tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((o hai) OR (co hai)). hieu ve cac ((duc van) OR (duc tan)) khanh tai cuc tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang ((o hai) or (co hai)). hieu ve cac ((duc van) OR (duc tan)) khanh tai cuc tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((o hai) or (co hai)). hieu ve cac ((duc van) OR (duc tan)) khanh tai cuc tre*.