Perhaps you should try some spelling variations:
dan hanh » dang hanh, dan khanh, dan thanh
thuc dan » thuc hanh, hoc dan, thuc vat
kho tang » cao tang
tu sach » thu sach, su sach, te sach
cua tre » cua te, cuu tre, cua triet
ky tang » ky nang, ky dang, ky trong
ve cac » va cac, vien cac
vi cua » vai cua, di cua
ve cam » ve cham, va cam, ve cai

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 tang) OR (kho tang)) xa hoi. hieu ((ve cam) or (ve cac)) thuc dan hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((ky tang) OR (kho tang)) xa hoi. hieu ((ve cam) OR (ve cac)) thuc dan hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((ky tang) OR (kho tang)) xa hoi. hieu ((ve cam) or (ve cac)) thuc dan hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach ((ky tang) OR (kho tang)) xa hoi. hieu ((ve cam) or (ve cac)) thuc dan hanh vi cua tre*.