Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
hanh tai » thanh tai, hang tai, han tai
van hanh » van thanh, ban hanh, van anh
xang dau » hang dau
luoc van » luoc can, luoc va, luc van
cam luoc » cam xuc, tom luoc, cam lo
tai cua » thai cua, tai cuc, tri cua
cua tre » cua te, cuu tre, cua triet
sach ky » sac ky, sach y, sach kem
hieu ve » hieu va
dau hoi » cau hoi, dai hoi, dan hoi
sach ty » sach y, sach tu, sach thu

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)) xang dau hoi. ((hieu ve) OR (hieu van)) cam luoc van hanh tai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach ky) OR (sach ty)) xang dau hoi. ((hieu ve) OR (hieu van)) cam luoc van hanh tai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach ky) or (sach ty)) xang dau hoi. ((hieu ve) OR (hieu van)) cam luoc van hanh tai cua tre".
• Adding a wildcard symbol may retrieve word variants: su ((sach ky) or (sach ty)) xang dau hoi. ((hieu ve) OR (hieu van)) cam luoc van hanh tai cua tre*.