enabling a radiobutton based on the selection of combobox?

Question

How to Enable a radio button based on combo box item?

For Example,

i have a combo box with 4 items  and two radiobuttons.if i select first item then the radio button 1 must be enabled at the same time radio button 2 must be in disable position.if i select other items in combo box then second radio button will enable and first will disable .please suggest me How can i do that in XAML.