Perhaps you should try some spelling variations:
khong thong » khong trong, thong thuong, phong chong
thanh trung » thanh tung
hieu lang » chieu sang, hieu quang, nhieu tang
trung cua » truong cua, trung tuan, trung cap
doan phan » doanh phan, toan phan, dan phan
doi hieu » doi chieu, doc hieu, doi hien
phan cau » phan dau, phan cac, phan tu

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

• If you are trying to use Boolean operators, they must be ALL CAPS: doi hieu lang - thanh trung cua ((khong thong) OR (thong thong)) doan phan cau~.
• Adding a wildcard symbol may retrieve word variants: doi hieu lang - thanh trung cua ((khong thong) or (thong thong)) doan phan cau*.