Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
van hanh » van thanh, ban hanh, van anh
hanh vai » hanh vi, hanh va, hanh tai
nang ma » tang ma, sang ma, mang may
cac tac » cac toc, cac bac, cac dac
te sac » te sach, te cac, te san
sac ky » cac ky, sai ky
vai va » mai va, dai va, hai va
thiet » thieu

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

• Performing a fuzzy search may retrieve terms with similar spellings: te sac ky ((nang ma) OR (nang cao)) hoi. hieu vien ((cac tac) or (dat nuoc)) van hanh vai va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: te sac ky ((nang ma) OR (nang cao)) hoi. hieu vien ((cac tac) OR (dat nuoc)) van hanh vai va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te sac ky ((nang ma) OR (nang cao)) hoi. hieu vien ((cac tac) or (dat nuoc)) van hanh vai va thiet".
• Adding a wildcard symbol may retrieve word variants: te sac ky ((nang ma) OR (nang cao)) hoi. hieu vien ((cac tac) or (dat nuoc)) van hanh vai va thiet*.