Perhaps you should try some spelling variations:
dan thanh » dang thanh, danh thanh, ban thanh
thanh doi » thanh loi, thanh moi, thanh do
thuc dan » thuc hanh, hoc dan, thuc vat
so sach » so sanh, bo sach, co sach
nang xa » nang x, lang xa, nang ma
van cam » van nam, van lam, van dam
van cau » van dau, van hau, van chat
y nang » ky nang, ly nang, v nang
cua tu » cua tuc, cua cu, cua te
cua su » qua su

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach y nang xa hoi. hieu ((van cam) or (van cau)) thuc dan thanh doi ((cua tu) OR (cua su))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach y nang xa hoi. hieu ((van cam) OR (van cau)) thuc dan thanh doi ((cua tu) OR (cua su)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach y nang xa hoi. hieu ((van cam) or (van cau)) thuc dan thanh doi ((cua tu) OR (cua su))".
• Adding a wildcard symbol may retrieve word variants: so sach y nang xa hoi. hieu ((van cam) or (van cau)) thuc dan thanh doi ((cua tu) OR (cua su))*.