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

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 don 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 don 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 don vi cau tren*.