Perhaps you should try some spelling variations:
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
duc tien » duc thien, luc tieng, thuc tien
tu sach » thu sach, su sach, te sach
ky dang » ky danh
mai hoa » mai khoa, ma hoa, dai hoa
hieu ve » hieu va, hieu van
han tai » hang tai, nhan tai, van tai
duc tre » duoc tren
ve cac » va cac, vien cac
va han » va phan, van han, va hanh

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 dang) OR (ky nang)) mai hoa. hieu ve cac nuoc va han tai ((duc tre) or (duc tien))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((ky dang) OR (ky nang)) mai hoa. hieu ve cac nuoc va han tai ((duc tre) OR (duc tien)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((ky dang) OR (ky nang)) mai hoa. hieu ve cac nuoc va han tai ((duc tre) or (duc tien))".
• Adding a wildcard symbol may retrieve word variants: tu sach ((ky dang) OR (ky nang)) mai hoa. hieu ve cac nuoc va han tai ((duc tre) or (duc tien))*.