Perhaps you should try some spelling variations:
dau tren » dau tien, dat tren, dau tieng
cau tren » cu tren, ca tren, cau treo
cuu tre » cua tre, cau treo
sach ty » sach y, sach tu, sach thu
tu sach » thu sach, su sach, te sach
ty nang » ky nang, ty xang, ty hang
hieu ve » hieu va, hieu van
ve cac » va cac, vien cac
cac su » cach su, cac sau, cac du
va dao » ca dao
dao vi » dao voi, dao ve, dao va
nang o » nang co, nang ho, nang ro
o hai » co hai, so hai, o lai
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 ty nang o hai. hieu ve cac su va dao vi ((cuu tre) or (((cau tren) OR (dau tren))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty nang o hai. hieu ve cac su va dao vi ((cuu tre) OR (((cau tren) OR (dau tren)))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ty nang o hai. hieu ve cac su va dao vi ((cuu tre) or (((cau tren) OR (dau tren))))".
• Adding a wildcard symbol may retrieve word variants: tu sach ty nang o hai. hieu ve cac su va dao vi ((cuu tre) or (((cau tren) OR (dau tren))))*.