Perhaps you should try some spelling variations:
san benh » sau benh, tai benh, so benh
ban benh » ba benh, ban banh, can benh
lang van » dang van, tang van, hoang van
cac quoc » cac nuoc, cac cuoc, cao quoc
qua cac » cua cac
tu sach » thu sach, su sach, te sach
sach ty » sach y, sach tu, sach thu
nang xa » nang x, lang xa, nang ma
cua tre » cua te, cuu tre, cua triet

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

• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty ((nang xa) OR (lang van)) hoi. hieu qua cac quoc ((ban benh) OR (san benh)) dai cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ty ((nang xa) or (lang van)) hoi. hieu qua cac quoc ((ban benh) OR (san benh)) dai cua tre~".
• Adding a wildcard symbol may retrieve word variants: tu sach ty ((nang xa) or (lang van)) hoi. hieu qua cac quoc ((ban benh) OR (san benh)) dai cua tre*.