Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
vien cac » vien bach, vien dai, vien da
doan vi » doan va, don vi, doan thi
va doan » va doanh, van doan, va dan
sach ky » sac ky, sach y, sach ty
tu sach » thu sach, su sach, te sach
vi cau » va cau, ve cau, di cau
ve cac » va cac
o hoi » co hoi, o hoc, o hai
x hoi » xa hoi, x ho, 5 hoi

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 ((x hoi) or (o hoi)). hieu ((ve cac) or (vien cac)) tu va doan vi cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((x hoi) OR (o hoi)). hieu ((ve cac) OR (vien cac)) tu va doan vi cau tren.
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((x hoi) or (o hoi)). hieu ((ve cac) or (vien cac)) tu va doan vi cau tren*.