Perhaps you should try some spelling variations:
sach ngan » sach ngon, sach nha, sach han
ngan cong » nganh cong, nganh nong, ngan hang
thuy hanh » thuc hanh, thuy anh, thuy canh
hanh tinh » hanh trinh, nhanh tinh, thanh tinh
hoc sach » hoc sinh, hoc cac, hoc anh
cong khi » cong thai, co khi, cong ha
khong he » hong ha, khong _, thong ha

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( hoc sach ngan cong khi đong luc ) or ( thuy hanh tinh ((khong khi) OR (khong he)) đong luc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( hoc sach ngan cong khi đong luc ) OR ( thuy hanh tinh ((khong khi) OR (khong he)) đong luc )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( hoc sach ngan cong khi đong luc ) or ( thuy hanh tinh ((khong khi) OR (khong he)) đong luc ))".
• Adding a wildcard symbol may retrieve word variants: (( hoc sach ngan cong khi đong luc ) or ( thuy hanh tinh ((khong khi) OR (khong he)) đong luc ))*.