Perhaps you should try some spelling variations:
sach thanh » sach tranh, sach tham, danh thanh
cong thai » cong hai, hong thai, cong thanh
ngan kho » nganh khoa, nhan khoa, ngang cho
kho khan » khoa kham, khoa than
vu sach » vu bach, vu khach
tu sach » thu sach, te sach, tu cach
su sach » so sach

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( vu sach thanh cong thai đong luc ) or ( ((tu sach) OR (su sach)) ngan kho khan đong luc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( vu sach thanh cong thai đong luc ) OR ( ((tu sach) OR (su sach)) ngan kho khan đong luc ))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( vu sach thanh cong thai đong luc ) or ( ((tu sach) OR (su sach)) ngan kho khan đong luc ))*".