Perhaps you should try some spelling variations:
toc sac » toc sach, toc san, hoc sach
nang ho » nang hoc, nang co, tang ho
nang ro » nang co, nang ra, nang rong
hieu va » lieu va, hieu qua
cua tre » cua te, cua triet, dua tren
cuu tre » cau tren, cau treo
sac ky » cac ky, sai ky
cac tu » cac thu, cach tu, cac du
va don » va dong, va doc, va do

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: toc sac ky ((nang ho) or (nang ro)) hoi. hieu va cac tu va don vi ((cua tre) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sac ky ((nang ho) OR (nang ro)) hoi. hieu va cac tu va don vi ((cua tre) OR (cuu tre)).
• Adding a wildcard symbol may retrieve word variants: toc sac ky ((nang ho) or (nang ro)) hoi. hieu va cac tu va don vi ((cua tre) or (cuu tre))*.