Perhaps you should try some spelling variations:
van nhanh » van thanh, van khanh, van nhan
cau tren » cu tren, dau tren, ca tren
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
thai cau » thai cao, toan cau, thai van
van hanh » van thanh, ban hanh, van anh
hieu ve » hieu va, hieu van
tu sai » tu bai, tu san, tu cai
sai ky » sac ky
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 sai ky nang ((o hoi) or (o hai)). hieu ve cac nuoc ((van nhanh) or (van hanh)) thai cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sai ky nang ((o hoi) OR (o hai)). hieu ve cac nuoc ((van nhanh) OR (van hanh)) thai cau tren.
• Adding a wildcard symbol may retrieve word variants: tu sai ky nang ((o hoi) or (o hai)). hieu ve cac nuoc ((van nhanh) or (van hanh)) thai cau tren*.