Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
cau tren » cu tren, dau tren, ca tren
sach ky » sach y, sach ty, sach kem
nang ma » tang ma, sang ma, nang cao
hieu ke » hieu kem, chieu ke, hieu ky
va hanh » va thanh, va danh, ban hanh
sac ky » cac ky, sai ky
ma hoi » mai hoi, xa hoi, ma hoa
ke cau » ket cau
vi cau » va cau, ve cau, di cau

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 ky) or (sac ky)) nang ma hoi. hieu ke cau truc ((va hanh) OR (van hanh)) vi cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc ((sach ky) OR (sac ky)) nang ma hoi. hieu ke cau truc ((va hanh) OR (van hanh)) vi cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc ((sach ky) or (sac ky)) nang ma hoi. hieu ke cau truc ((va hanh) OR (van hanh)) vi cau tren".
• Adding a wildcard symbol may retrieve word variants: hoc ((sach ky) or (sac ky)) nang ma hoi. hieu ke cau truc ((va hanh) OR (van hanh)) vi cau tren*.