Perhaps you should try some spelling variations:
vu sach » vu bach, vu khach
va hanh » van hanh, va thanh, va danh
cac bac » cac bai, cac ban, cac cach
cac tac » cac toc, cac dac, cac tai
hieu va » lieu va, hieu qua
lang ha » long ha
ky lang » ky nang, ky dang, ky tang
su sach » so sach
cua tre » cua te, cuu tre, cua triet
ha hoi » hoa hoi, ha noi, xa hoi
vi cua » vai cua, di cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((vu sach) or (su sach)) ky lang ha hoi. hieu va ((cac tac) OR (cac bac)) va hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((vu sach) OR (su sach)) ky lang ha hoi. hieu va ((cac tac) OR (cac bac)) va hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((vu sach) or (su sach)) ky lang ha hoi. hieu va ((cac tac) OR (cac bac)) va hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: ((vu sach) or (su sach)) ky lang ha hoi. hieu va ((cac tac) OR (cac bac)) va hanh vi cua tre*.