Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
quoc ban » quoc bao, quoc lan, quoc quan
lanh dai » lanh dao, lanh hai, vanh dai
lang dai » lang hai, lang mai, lang chai
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
ky dang » ky nang, ky danh
dang xa » dang xay, lang xa, dang ha
duc van » duc va, duc tan, duc manh
cua tre » cua te, cuu tre, cua triet

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ky dang xa hoi. hieu van nam ((quoc ban) or (duc van)) ((lanh dai) or (lang dai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky dang xa hoi. hieu van nam ((quoc ban) OR (duc van)) ((lanh dai) OR (lang dai)) cua tre.
• Adding a wildcard symbol may retrieve word variants: tu sach ky dang xa hoi. hieu van nam ((quoc ban) or (duc van)) ((lanh dai) or (lang dai)) cua tre*.