Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
toc sach » hoc sach, doc sach, thuoc sach
duc van » duc va, duc tan, duc manh
cac duc » cac du, cao duc, cac dac
hieu ve » hieu va, hieu van
mai hoi » mai khoi, dai hoi, lai hoi
cua tre » cua te, cuu tre, cua triet
ve cac » va cac, vien cac
v nang » va nang, vu nang, van nang
vi cua » vai cua, di cua

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: ((te sach) OR (toc sach)) v nang ((ma hoa) OR (mai hoi)). hieu ve cac duc van hanh vi cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) OR (toc sach)) v nang ((ma hoa) or (mai hoi)). hieu ve cac duc van hanh vi cua tre~".
• Adding a wildcard symbol may retrieve word variants: ((te sach) OR (toc sach)) v nang ((ma hoa) or (mai hoi)). hieu ve cac duc van hanh vi cua tre*.