Perhaps you should try some spelling variations:
thanh tai » thanh hai, thanh toan, doanh tai
hoc viet » hoc hien
hanh tai » hang tai, han tai, hinh tai
hieu van » hieu va, thien van, lieu va
van dam » van nam, van dao, van dau
nang xa » nang x, nang ma, mang xa
lang xa » lang ha, dang xay, lang van
dam tu » nam tu, cam tu, tam tu
sac ky » cac ky, sai ky
so sac » so sach, so dac

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sac ky ((nang xa) or (lang xa)) hoi. hieu van dam tu va ((hanh tai) OR (thanh tai)) hoc viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sac ky ((nang xa) OR (lang xa)) hoi. hieu van dam tu va ((hanh tai) OR (thanh tai)) hoc viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sac ky ((nang xa) or (lang xa)) hoi. hieu van dam tu va ((hanh tai) OR (thanh tai)) hoc viet".
• Adding a wildcard symbol may retrieve word variants: so sac ky ((nang xa) or (lang xa)) hoi. hieu van dam tu va ((hanh tai) OR (thanh tai)) hoc viet*.