Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
van hanh » van thanh, ban hanh, van anh
vien cac » vien bach, vien dai, vien da
va hanh » va thanh, va danh, ban hanh
cac thu » cach thuc, cac thoi
sach ly » sach y, sach lo, sach hay
sach ty » sach y, sach tu, sach thu
cua tre » cua te, cuu tre, cua triet
nang o » nang co, nang ho, nang ro
vi cua » vai cua, di cua
o hoi » co hoi, o hoc, o hai

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 ly) OR (sach ty)) nang o hoi. hieu vien cac thu ((va hanh) or (van hanh)) vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach ly) OR (sach ty)) nang o hoi. hieu vien cac thu ((va hanh) OR (van hanh)) vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach ly) OR (sach ty)) nang o hoi. hieu vien cac thu ((va hanh) or (van hanh)) vi cua tre".
• Adding a wildcard symbol may retrieve word variants: su ((sach ly) OR (sach ty)) nang o hoi. hieu vien cac thu ((va hanh) or (van hanh)) vi cua tre*.