Perhaps you should try some spelling variations:
vien cac » vien bach, vien dai, vien da
tu sach » thu sach, te sach, tu cach
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cuu tre, cua triet
nang ma » tang ma, sang ma, nang cao
su sach » so sach, vu sach
tac va » tac da, tac xa, tuc va
vi cua » vai cua, di cua
ve cac » va cac

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