Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
hieu ve » hieu va, hieu van
tu sach » thu sach, su sach, te sach
v nang » va nang, vu nang, van nang
ho hoi » hoc hoi, hoa hoi, hoi hoi
y nang » ky nang, ly nang, may nang
cac su » cach su, cac sau, cac du
dao vi » dao voi, dao ve, dao li
dao va » dao van, tao va, do va
ve cac » va cac, vien cac
su va » su van, tu va

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 ((y nang) or (v nang)) ho hoi. hieu ve cac su va ((dao vi) OR (dao va)) cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((y nang) OR (v nang)) ho hoi. hieu ve cac su va ((dao vi) OR (dao va)) cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((y nang) or (v nang)) ho hoi. hieu ve cac su va ((dao vi) OR (dao va)) cau tren".
• Adding a wildcard symbol may retrieve word variants: tu sach ((y nang) or (v nang)) ho hoi. hieu ve cac su va ((dao vi) OR (dao va)) cau tren*.