Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
hang tai » hang va, dung tai
hanh tai » thanh tai, han tai, hinh tai
nang dau » hang dau, xang dau, nang du
nam luc » nang luc, nhan luc, nam thuc
luc van » luoc van, luu van, duc van
cua tre » cua te, cuu tre, cua triet
dau hoi » cau hoi, dai hoi, dan hoi
sach tu » sach thu, cach tu, sach ty
sac ky » cac ky, sai ky

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

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