Perhaps you should try some spelling variations:
nang cau » nang cao, hang cau, nang dau
tinh tai » trinh tai, tinh thai, tinh hai
sach ky » sac ky, sach y, sach kem
tai cua » thai cua, tai cuc, tri cua
cua tre » cua te, cuu tre, cua triet
hieu ve » hieu va, hieu van
sach ty » sach y, sach tu, sach thu
toc va » toc ta, tuc va, loc va
ve cac » va cac, vien cac

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

• Performing a fuzzy search may retrieve terms with similar spellings: su ((sach ky) or (sach ty)) nang cau hoi. hieu ve cac ((toc va) OR (hoc va)) tinh tai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach ky) OR (sach ty)) nang cau hoi. hieu ve cac ((toc va) OR (hoc va)) tinh tai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach ky) or (sach ty)) nang cau hoi. hieu ve cac ((toc va) OR (hoc va)) tinh tai cua tre".
• Adding a wildcard symbol may retrieve word variants: su ((sach ky) or (sach ty)) nang cau hoi. hieu ve cac ((toc va) OR (hoc va)) tinh tai cua tre*.