Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
hac truc » hoc truc, hang truc, sach truc
sach ky » sach y, sach ty, sach kem
hieu va » lieu va, hieu qua
truc va » thuc va, thuc vat, trung va
va danh » va dinh, va dan, va hanh
danh vi » hanh vi, dinh vi, danh di
cuu tre » cua tre, cau treo
sac ky » cac ky, sai ky
va hac » van hac, va khac, va cac
x hoi » xa hoi, o hoi, x ho

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) OR (sac ky)) nang x hoi. hieu va hac truc va danh vi ((cuu tre) or (cau tren))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ky) OR (sac ky)) nang x hoi. hieu va hac truc va danh vi ((cuu tre) OR (cau tren)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach ky) OR (sac ky)) nang x hoi. hieu va hac truc va danh vi ((cuu tre) or (cau tren))".
• Adding a wildcard symbol may retrieve word variants: tu ((sach ky) OR (sac ky)) nang x hoi. hieu va hac truc va danh vi ((cuu tre) or (cau tren))*.