Perhaps you should try some spelling variations:
nguoi san » nguoi tay, nguoi dao, nguoi ma
nuoc san » nuoc luan, nuoc quan, nuoc sach
cao hoc » co hoc, cho hoc, chat hoc
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
sac ky » cac ky
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: vu ((sac ky) or (sai ky)) nang cao hoc. hieu ve cac ((nuoc san) OR (nguoi san)) hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: vu ((sac ky) OR (sai ky)) nang cao hoc. hieu ve cac ((nuoc san) OR (nguoi san)) hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "vu ((sac ky) or (sai ky)) nang cao hoc. hieu ve cac ((nuoc san) OR (nguoi san)) hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: vu ((sac ky) or (sai ky)) nang cao hoc. hieu ve cac ((nuoc san) OR (nguoi san)) hanh vi cua tre*.