Perhaps you should try some spelling variations:
ban thanh » ban hanh, ban hang
thanh hai » thanh phan, thanh hoa, thanh san
cuu tre » cau tren, cau treo
duc ban » duc tan, duc van, dua ban
ky dang » ky nang, ky danh
mau hoi » cau hoi, mai hoi, mau hop
cua tre » cua te, cua triet, dua tren
hieu ve » hieu va, hieu van
cac duc » cac du, cao duc, cac dac
su sac » su sach, su cac, su xac
sac ky » cac ky, sai ky
mau ho » mau hop, mau co, mau do
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: su sac ky dang ((mau hoi) or (mau ho)). hieu ve cac duc ban thanh hai ((cua tre) OR (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sac ky dang ((mau hoi) OR (mau ho)). hieu ve cac duc ban thanh hai ((cua tre) OR (cuu tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sac ky dang ((mau hoi) or (mau ho)). hieu ve cac duc ban thanh hai ((cua tre) OR (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: su sac ky dang ((mau hoi) or (mau ho)). hieu ve cac duc ban thanh hai ((cua tre) OR (cuu tre))*.