Perhaps you should try some spelling variations:
sach thue » sach thieu, sach tham, cach thuc
cam thuc » am thuc, nam thuc, cam thu
hieu van » hieu va, thien van, lieu va
sach thu » sach thieu, sach tham, cach thuc
cau hai » cau hoi, cau hat, cau ha
dau hai » dai hai, dau ha, dao hai
van cam » van nam, van lam, van cau
thuc va » thuc vat, thuc dan, thuc day
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.

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