Perhaps you should try some spelling variations:
hanh thai » nhanh thai, hinh thai, hanh tai
thai cua » than cua, tai cuc, tri cua
van hanh » van thanh, ban hanh, van anh
duc van » duc va, duc tan, duc manh
cac duc » cac du, cao duc, cac dac
hieu va » lieu va, hieu qua
cua tre » cua te, cuu tre, cua triet
sach ky » sac ky, sach ty, sach kem
o hoi » co hoi, o hai, o hoa
o hoc » co hoc, mo hoc, so hoc

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

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