Perhaps you should try some spelling variations:
cham hoc » cham soc, chat hoc, cham hoi
nang xa » nang x, lang xa, nang ma
hieu va » hieu qua
han tai » hang tai, nhan tai, toan tai
van tai » von tai, van tuan
tu sac » tu sach, tu cac, tu san
sac ky » cac ky, sai ky
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: tu sac ky nang xa hoi. ((hieu va) OR (lieu va)) cham hoc va ((han tai) or (van tai)) va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sac ky nang xa hoi. ((hieu va) OR (lieu va)) cham hoc va ((han tai) OR (van tai)) va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sac ky nang xa hoi. ((hieu va) OR (lieu va)) cham hoc va ((han tai) or (van tai)) va thiet".
• Adding a wildcard symbol may retrieve word variants: tu sac ky nang xa hoi. ((hieu va) OR (lieu va)) cham hoc va ((han tai) or (van tai)) va thiet*.