Perhaps you should try some spelling variations:
truoc cach » cuoc cach, truoc cang
khan thong » khap thong, khau thong, nhan thong
thuc bach » truc bach, thuoc sach, thuc hanh
thuc cach » thuoc sach, thuc hanh, tuc cac
kho khan » khoa kham, khoa than
tu sach » thu sach, su sach, te sach
so sach » so sanh, bo sach, co sach

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) or (so sach)) bai ((thuc bach) or (((truoc cach) OR (thuc cach)))) kho khan thong~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (so sach)) bai ((thuc bach) OR (((truoc cach) OR (thuc cach)))) kho khan thong*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (so sach)) bai ((thuc bach) or (((truoc cach) OR (thuc cach)))) kho khan thong*".