Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
va thanh » gia thanh, ban thanh, va tinh
va hanh » van hanh, va danh, ban hanh
sach ky » sac ky, sach y, sach kem
hieu te » hieu ve, hien te, hieu he
sach ty » sach y, sach tu, sach thu
ve cau » ke cau, va cau, ve cac
te ban » te bao
x hoi » xa hoi, o hoi, x ho

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

• Performing a fuzzy search may retrieve terms with similar spellings: su ((sach ky) OR (sach ty)) nang x hoi. hieu te ban do ((va hanh) or (va thanh)) ve cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach ky) OR (sach ty)) nang x hoi. hieu te ban do ((va hanh) OR (va thanh)) ve cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach ky) OR (sach ty)) nang x hoi. hieu te ban do ((va hanh) or (va thanh)) ve cau tren".
• Adding a wildcard symbol may retrieve word variants: su ((sach ky) OR (sach ty)) nang x hoi. hieu te ban do ((va hanh) or (va thanh)) ve cau tren*.