Perhaps you should try some spelling variations:
cau tren » cu tren, dau tren, ca tren
khao tuc » khao phuc, dao tuc, khao cuu
hieu va » lieu va, hieu qua
sach ky » sac ky, sach y, sach ty
va danh » va dan, va hanh, dia danh
va dinh » van dinh, va kinh, va tinh
tu sach » thu sach, su sach, te sach
vi cau » va cau, ve cau, di cau
o hoi » co hoi, o hoc, o hai
x hoi » xa hoi, x ho, 5 hoi

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ky nang ((x hoi) OR (o hoi)). hieu va khao tuc ((va danh) or (va dinh)) vi cau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((x hoi) OR (o hoi)). hieu va khao tuc ((va danh) OR (va dinh)) vi cau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang ((x hoi) OR (o hoi)). hieu va khao tuc ((va danh) or (va dinh)) vi cau tren".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((x hoi) OR (o hoi)). hieu va khao tuc ((va danh) or (va dinh)) vi cau tren*.