Perhaps you should try some spelling variations:
thanh cau » thanh chau, thanh mau, nhanh cau
van thanh » ban thanh, van tuan
van nhanh » van hanh, van khanh, van nhan
cau tren » cu tren, dau tren, ca tren
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
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 ky nang ((o hoi) or (o hai)). hieu ve cac nuoc ((van nhanh) or (van thanh)) thanh cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((o hoi) OR (o hai)). hieu ve cac nuoc ((van nhanh) OR (van thanh)) thanh cau tren.
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((o hoi) or (o hai)). hieu ve cac nuoc ((van nhanh) or (van thanh)) thanh cau tren*.