Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
sach dau » sach dao, sach dat, sach mau
nano cau » nang cau, bang cau, nano va
sach day » sach dao, sach dat, sach hay
hanh va » hang va, hanh vi
duc van » duc va, duc tan, duc manh
cua tre » cua te, cuu tre, cua triet
va cua » va chua, via cua, ca cua
ve 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: su ((sach day) OR (sach dau)) nano cau hoi. hieu ((ve cac) or (va cac)) duc van hanh va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach day) OR (sach dau)) nano cau hoi. hieu ((ve cac) OR (va cac)) duc van hanh va cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach day) OR (sach dau)) nano cau hoi. hieu ((ve cac) or (va cac)) duc van hanh va cua tre".
• Adding a wildcard symbol may retrieve word variants: su ((sach day) OR (sach dau)) nano cau hoi. hieu ((ve cac) or (va cac)) duc van hanh va cua tre*.