Perhaps you should try some spelling variations:
toc sac » toc sach, toc san, hoc sach
cua tre » cua te, cua triet, dua tren
cac thu » cach thuc, cac thoi
hieu ve » hieu va, hieu van
cuu tre » cau tren, cau treo
nang ho » nang hoc, nang co, tang ho
nang ra » nang ma, lang ra, nang ro
sac ky » cac ky, sai ky
thu va » thuc va, thue va, tu va
va don » va dong, va doc, va do
ve cac » va cac, vien cac

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 ra)) hoi. hieu ve cac thu 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 ra)) hoi. hieu ve cac thu va don vi ((cua tre) OR (cuu tre)).
• Adding a wildcard symbol may retrieve word variants: toc sac ky ((nang ho) or (nang ra)) hoi. hieu ve cac thu va don vi ((cua tre) or (cuu tre))*.