Perhaps you should try some spelling variations:
vien bac » vien bach, mien bac, tien bac
vien cac » vien bach, vien dai, vien da
tu sach » thu sach, te sach, tu cach
danh va » doanh va, hanh va, anh va
va danh » va dinh, va dan, va hanh
cua tre » cua te, cuu tre, cua triet
su sach » so sach, vu sach
cao va » cao van, tao va, co va
va cua » va chua, via cua, ca cua
x hoi » xa hoi, o hoi, x ho

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) or (su sach)) ky nang x hoi. hieu ((vien bac) OR (vien cac)) cao va danh va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (su sach)) ky nang x hoi. hieu ((vien bac) OR (vien cac)) cao va danh va cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (su sach)) ky nang x hoi. hieu ((vien bac) OR (vien cac)) cao va danh va cua tre".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (su sach)) ky nang x hoi. hieu ((vien bac) OR (vien cac)) cao va danh va cua tre*.