Perhaps you should try some spelling variations:
dau tren » dau tien, dat tren, dau tieng
van hanh » van thanh, ban hanh, van anh
nam truc » nam truoc, nam thuc, nam trung
cam truc » cau truc, lam truoc, nam truoc
hieu va » lieu va, hieu qua
sang ma » tang ma, sang tao, mang may
nang ma » tang ma, nang cao, mang may
hanh va » hang va, hanh vi
va dau » va dao

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu cac ky ((sang ma) or (nang ma)) hoi. hieu va ((cam truc) or (nam truc)) van hanh va dau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu cac ky ((sang ma) OR (nang ma)) hoi. hieu va ((cam truc) OR (nam truc)) van hanh va dau tren.
• Adding a wildcard symbol may retrieve word variants: tu cac ky ((sang ma) or (nang ma)) hoi. hieu va ((cam truc) or (nam truc)) van hanh va dau tren*.