Perhaps you should try some spelling variations:
ban thanh » ban hang
thu sach » tu sach, thuat sach, thuoc sach
hieu van » hieu va, thien van, lieu va
ban hanh » ban hang
cau tren » cu tren, dau tren, ca tren
sach ky » sac ky, sach y, sach ty
mai hoi » mai khoi, dai hoi, lai hoi
nam dua » nam da, nam cua, nam mua
vai cau » va cau, van cau, vai cac

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

• Performing a fuzzy search may retrieve terms with similar spellings: thu sach ky nang ((mai hoi) or (ma hoa)). hieu van nam dua ((ban thanh) OR (ban hanh)) vai cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ky nang ((mai hoi) OR (ma hoa)). hieu van nam dua ((ban thanh) OR (ban hanh)) vai cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach ky nang ((mai hoi) or (ma hoa)). hieu van nam dua ((ban thanh) OR (ban hanh)) vai cau tren".
• Adding a wildcard symbol may retrieve word variants: thu sach ky nang ((mai hoi) or (ma hoa)). hieu van nam dua ((ban thanh) OR (ban hanh)) vai cau tren*.