Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
dien cua » dieu cua, dien cuc, dien cu
va nhanh » va thanh, va hanh, va nganh
cau duc » cao duc, cau luc, chu duc
va nhan » van nhan, ca nhan, va phan
cua tre » cua te, cuu tre, cua triet
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
ve cau » ke cau, va cau, ve cac
o hai » co hai, so hai, o lai
o hoi » co hoi, o hoc, o hoa

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach ky nang ((o hoi) or (o hai)). hieu ve cau duc ((va nhanh) OR (va nhan)) dien cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky nang ((o hoi) OR (o hai)). hieu ve cau duc ((va nhanh) OR (va nhan)) dien cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky nang ((o hoi) or (o hai)). hieu ve cau duc ((va nhanh) OR (va nhan)) dien cua tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ky nang ((o hoi) or (o hai)). hieu ve cau duc ((va nhanh) OR (va nhan)) dien cua tre*.