Perhaps you should try some spelling variations:
khau thong » khau thuong, khap thong, khau tong
phu thong » pho thong, phap thong, phan thong
giao khoa » bia khoa, lao khoa, go khoa
sach bai » sach dao, cac bai, sach xa
tai giao » mai giao, dai giao, tai giai
su sach » so sach, vu sach
bai tai » bai tap, ban tai, dai tai

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 bai tai giao khoa ((phu thong) or (khau thong))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach bai tai giao khoa ((phu thong) OR (khau thong)).
• Adding a wildcard symbol may retrieve word variants: su sach bai tai giao khoa ((phu thong) or (khau thong))*.