Perhaps you should try some spelling variations:
thieu xanh » chieu xanh, hieu manh, thien anh
hanh trang » thanh trung, hanh trinh, minh trang
nhung cong » dung cong, thong cong, hang cong
hoc thieu » toc thieu, hoc hien
cua nhung » va nhung
tap toan » tap quan, bai toan
tap doan » tap quan

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: hoc thieu xanh - ((hanh trang) OR (canh tranh)) cua nhung cong ((tap toan) OR (tap doan)) cau~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc thieu xanh - ((hanh trang) OR (canh tranh)) cua nhung cong ((tap toan) or (tap doan)) cau~".
• Adding a wildcard symbol may retrieve word variants: hoc thieu xanh - ((hanh trang) OR (canh tranh)) cua nhung cong ((tap toan) or (tap doan)) cau*.