Perhaps you should try some spelling variations:
vien cac » vien bach, vien dai, vien da
thanh vi » thanh va, thanh ve, nhanh vi
sach ty » sach y, sach tu, sach thu
truc va » thuc va, thuc vat, trung va
su sach » so sach, vu sach
su tien » su kien, su hien, tu tieng
ve cac » va cac
xang x » nang x
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 ty xang x hoi. hieu ((ve cac) or (vien cac)) truc va ((thanh vi) OR (hanh vi)) su tien~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ty xang x hoi. hieu ((ve cac) OR (vien cac)) truc va ((thanh vi) OR (hanh vi)) su tien.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ty xang x hoi. hieu ((ve cac) or (vien cac)) truc va ((thanh vi) OR (hanh vi)) su tien".
• Adding a wildcard symbol may retrieve word variants: su sach ty xang x hoi. hieu ((ve cac) or (vien cac)) truc va ((thanh vi) OR (hanh vi)) su tien*.