Perhaps you should try some spelling variations:
vien cac » vien bach, vien dai, vien da
hanh va » hang va, hanh vi
hanh ve » hanh vi, hanh kem
su sach » so sach, vu sach
ca tren » cau tren, cu tren, la tren
y hang » ly hang, ty hang, yu hang
ve cac » va cac
hang x » nang x, hoang xa, chang xu
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 y hang x hoi. hieu ((ve cac) OR (vien cac)) duc va ((hanh ve) or (hanh va)) ca tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach y hang x hoi. hieu ((ve cac) OR (vien cac)) duc va ((hanh ve) OR (hanh va)) ca tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach y hang x hoi. hieu ((ve cac) OR (vien cac)) duc va ((hanh ve) or (hanh va)) ca tren".
• Adding a wildcard symbol may retrieve word variants: su sach y hang x hoi. hieu ((ve cac) OR (vien cac)) duc va ((hanh ve) or (hanh va)) ca tren*.