单选按钮没有使用Ajax发送正确的值

I have a group of radiobuttons listing all the available grades in a school. The onchange event fires an Ajax request that returns all available subjects for that particular grade and displays them in a listbox. Unfortunately it always returns the value of the first radio button in the group. Everything else still works except for the wrong radio button value being passed.I have a group of radiobuttons listing all the