Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
cac quoc » cac nuoc, cac cuoc, cao quoc
manh hai » lanh hai, minh hai, thanh hai
quoc ban » quoc bao, quoc lan, quoc quan
anh hai » lanh hai, anh thai, anh bai
cua tre » cua te, cuu tre, cua triet
hieu ve » hieu va, hieu van
ty hang » ly hang, ty xang, thi hang
ty nang » ky nang, ty xang, ly nang
ve cac » va cac, vien cac

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

• Performing a fuzzy search may retrieve terms with similar spellings: thu sach ((ty nang) OR (ty hang)) xa hoi. hieu ve cac quoc ban ((anh hai) or (manh hai)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ((ty nang) OR (ty hang)) xa hoi. hieu ve cac quoc ban ((anh hai) OR (manh hai)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach ((ty nang) OR (ty hang)) xa hoi. hieu ve cac quoc ban ((anh hai) or (manh hai)) cua tre".
• Adding a wildcard symbol may retrieve word variants: thu sach ((ty nang) OR (ty hang)) xa hoi. hieu ve cac quoc ban ((anh hai) or (manh hai)) cua tre*.