Perhaps you should try some spelling variations:
ban hang » ngan hang
cac xuc » cam xuc, cac nuoc, chat xuc
tai cua » thai cua, tai cuc, tri cua
cua tre » cua te, cuu tre, cua triet
sach ky » sach y, sach ty, sach kem
hieu ve » hieu va, hieu van
cao hoc » co hoc, cho hoc, chat hoc
sac ky » cac ky, sai ky
ve cac » va cac, vien cac

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu ((sach ky) or (sac ky)) nang cao hoc. hieu ve cac xuc ((ban hanh) OR (ban hang)) tai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ky) OR (sac ky)) nang cao hoc. hieu ve cac xuc ((ban hanh) OR (ban hang)) tai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach ky) or (sac ky)) nang cao hoc. hieu ve cac xuc ((ban hanh) OR (ban hang)) tai cua tre".
• Adding a wildcard symbol may retrieve word variants: tu ((sach ky) or (sac ky)) nang cao hoc. hieu ve cac xuc ((ban hanh) OR (ban hang)) tai cua tre*.