Using JS To Change Css Class?

I have a form with a list of things. The number of things in the list is variable, depending on certain factor, different things, different numbers of things. Next to each thing is a radio button.

There is a question with two radio buttons, "yes" and "no".

When "no" is selected, I want the radio buttons to be disabled, and the color of the text to change to gray.

For the radio buttons, I have a simple JS function:

javascript Code:

function enableCFFID()
{
document.cartform.cffid.disabled=false;
}

[Code].....

For the test that goes with each thing, obviously I don't want to have to assign unique ID (perhaps in a span tag that encloses the text). I would want a common name for all of them.

But this would mean I can't use getElementById.

What other method can I use to change the class for a group of span tags who's number is variable?