Perhaps you should try some spelling variations:
sang mai » sang ma, sang tai, lang mai
ky sang » ky nang, ky dang, ky tang
mai hoi » mai khoi, dai hoi, lai hoi
hieu ve » hieu va, hieu van
duc van » duc va, duc tan, duc manh
hoc can » hoc dan, hoc cao, hoc cac
cua tre » cua te, cuu tre, cua triet
te cac » tu cac, te cao, de cac
ve cac » va cac, vien cac
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: te cac ky sang mai hoi. hieu ve cac ((duc van) or (hoc can)) hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te cac ky sang mai hoi. hieu ve cac ((duc van) OR (hoc can)) hanh vi cua tre.
• Adding a wildcard symbol may retrieve word variants: te cac ky sang mai hoi. hieu ve cac ((duc van) or (hoc can)) hanh vi cua tre*.