Perhaps you should try some spelling variations:
ban thanh » ban hang
hieu van » hieu va, thien van, lieu va
ban hanh » ban hang
vu sach » vu bach, su sach, vu khach
lai cua » dai cua, hai cua, lai chau
vai cua » dai cua, hai cua, bai cua
sach ky » sac ky, sach y, sach ty
nam qua » nam quan, nam cua, nam mua
sang ma » tang ma, nang ma, sang tao
ky sang » ky nang, ky dang, ky tang
ma hoi » mai hoi, xa hoi, ma hoa

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

• If you are trying to use Boolean operators, they must be ALL CAPS: vu sach ky sang ma hoi. hieu van nam qua ((ban thanh) OR (ban hanh)) ((vai cua) OR (lai cua)) tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "vu sach ky sang ma hoi. hieu van nam qua ((ban thanh) OR (ban hanh)) ((vai cua) or (lai cua)) tre~".
• Adding a wildcard symbol may retrieve word variants: vu sach ky sang ma hoi. hieu van nam qua ((ban thanh) OR (ban hanh)) ((vai cua) or (lai cua)) tre*.