Perhaps you should try some spelling variations:
tao khoi » thao khoa, lao khoa, tao boi
hieu va » lieu va, hieu qua
hoc can » hoc dan, hoc cao, hoc cac
duc van » duc va, duc tan, duc manh
cua tre » cua te, cuu tre, cua triet
tao hoi » tao boi, tay hoi, thao hoc
ky sang » ky nang, ky dang, ky tang
sac ky » cac ky, sai ky
vi cua » vai cua, di cua
te sac » te sach, te cac, te san

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

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