Perhaps you should try some spelling variations:
toi hoat » toan hoat, thi hoa, thi hoan
cham hoc » cham soc, chat hoc, cham hoi
so sach » so sanh, bo sach, co sach
sach ky » sac ky, sach y, sach ty
ky sang » ky nang, ky dang, ky tang
toan ho » toan hoc, toan khoa, toan cao
hieu ve » hieu va, hieu van
ve cham » va cham, ve chat, vu cham
va danh » va dinh, va dan, va hanh
danh vi » hanh vi, dinh vi, danh di
vi cua » vai cua, di cua
cua te » cua tu

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach ky sang ((toan ho) or (toi hoat)). hieu ve cham hoc va danh vi cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ky sang ((toan ho) OR (toi hoat)). hieu ve cham hoc va danh vi cua te.
• Adding a wildcard symbol may retrieve word variants: so sach ky sang ((toan ho) or (toi hoat)). hieu ve cham hoc va danh vi cua te*.