javascript for enabling and disabling combo boxes depending value of radiobutton

Question

Hi Friends,

 I am developing an web application. here in an web form i need am using two radio buttons and two combo boxes say r1and r2 for radio and c1 and c2 for comboboxes.

Here my web form inherits from master page. I need to enable c1 when r1 is checked and c2 when r2 is checked.

i need to write javascript for this. how can i do this.

Regards

Rajath