Perhaps you should try some spelling variations:
dua tren » dung tren
toc sac » toc sach, toc san, hoc sach
cach tu » cach thuc
ve cach » va cach, ve cac, ve canh
hieu ve » hieu va, hieu van
nang co » nang cao, nang doc, nang noi
nang ho » nang hoc, tang ho, nang cao
cuu tre » cua tre, cau tren, cau treo
sac ky » cac ky, sai ky
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 co)) hoi. hieu ve cach tu va don vi ((dua tren) or (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sac ky ((nang ho) OR (nang co)) hoi. hieu ve cach tu va don vi ((dua tren) OR (cuu tre)).
• Adding a wildcard symbol may retrieve word variants: toc sac ky ((nang ho) or (nang co)) hoi. hieu ve cach tu va don vi ((dua tren) or (cuu tre))*.