Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
den hanh » den thanh, dan hanh, deu hanh
tu sach » thu sach, te sach, tu cach
su sach » so sach, vu sach
nang ma » tang ma, sang ma, nang cao
xe hanh » ve hanh, de thanh, deu hanh
tai cua » thai cua, tai cuc, tri cua
cua tre » cua te, cuu tre, cua triet
ma hoi » mai hoi, xa hoi, ma hoa

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