Perhaps you should try some spelling variations:
thanh va » thanh van, hanh va, thanh ha
truc gia » truc giac, tuc gia, thuc giai
sach ty » sach y, sach thu, xach tay
sach tu » sach thu, cach tu, sach uu
su tien » su kien, su hien, tu tieng
xang o » lang o, tang o, dang o
ve cau » ke cau, ve cac, le cau
va cau » van cau, va cac, va dau
o hoi » co hoi, o hoc, o hai

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

• Performing a fuzzy search may retrieve terms with similar spellings: so ((sach ty) or (sach tu)) xang o hoi. hieu ((ve cau) OR (va cau)) truc gia thanh va su tien~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so ((sach ty) OR (sach tu)) xang o hoi. hieu ((ve cau) OR (va cau)) truc gia thanh va su tien.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so ((sach ty) or (sach tu)) xang o hoi. hieu ((ve cau) OR (va cau)) truc gia thanh va su tien".
• Adding a wildcard symbol may retrieve word variants: so ((sach ty) or (sach tu)) xang o hoi. hieu ((ve cau) OR (va cau)) truc gia thanh va su tien*.