Perhaps you should try some spelling variations:
van khanh » van thanh, van anh, van phan
dua tren » dung tren
thai dua » thai cua, thi dua, thai doan
van hanh » van thanh, ban hanh, van anh
cac xuc » cam xuc, cac nuoc, chat xuc
tu sach » thu sach, su sach, te sach
sach ty » sach y, sach tu, sach thu
ty hang » ly hang, ty xang, thi hang
hieu ve » hieu va, hieu van
ve cac » va cac, vien cac
o hai » co hai, so hai, o lai
o hoi » co hoi, o hoc, o hoa

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 ty hang ((o hoi) or (o hai)). hieu ve cac xuc ((van khanh) or (van hanh)) thai dua tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty hang ((o hoi) OR (o hai)). hieu ve cac xuc ((van khanh) OR (van hanh)) thai dua tren.
• Adding a wildcard symbol may retrieve word variants: tu sach ty hang ((o hoi) or (o hai)). hieu ve cac xuc ((van khanh) or (van hanh)) thai dua tren*.