The disease malaria,which is spread by mosquitoes,kills over

The disease malaria,which is spread by mosquitoes,kills over one million children yearly.______,
______,according to the United Nations,hunger and malnutrition claim ten million lives each year.
A.However B.On the contrary C.On top of this D.As a result
答案为什么是C呢？我也选的 A转折，更强调下一句！on top of this 是基于......的意思！