Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
cac nuoc » cap nuoc, hoc nuoc, cua nuoc
hanh hai » thanh hai, nhanh hai, hanh tai
hang hai » hoang hai, hang tai, thanh hai
su sach » so sach, vu sach
sach ky » sac ky, sach y, sach ty
cuu tre » cua tre, cau tren, cau treo
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: su sach ky nang x hoi. hieu van ((cac nuoc) OR (dat nuoc)) va ((hanh hai) or (hang hai)) cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky nang x hoi. hieu van ((cac nuoc) OR (dat nuoc)) va ((hanh hai) OR (hang hai)) cuu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky nang x hoi. hieu van ((cac nuoc) OR (dat nuoc)) va ((hanh hai) or (hang hai)) cuu tre".
• Adding a wildcard symbol may retrieve word variants: su sach ky nang x hoi. hieu van ((cac nuoc) OR (dat nuoc)) va ((hanh hai) or (hang hai)) cuu tre*.