how do I suppress certain HTML input fields based on drop down selection?

how do I suppress certain HTML input fields based on drop down selection?

Hypothetical situation:
I have a form that has 11 fields, fields 1 through 11.
Let's say field 1 is a drop down with 3 values: "A", "B", "C"
How do I use HTML/JavaScript to say that:
if user selects "A", then only fields 2,3,4 are editable (the rest are not)
if user selects "B", then only fields 5,6,7,8 are editable (the rest are not)
if user selects "C", then only fields 9,10,11 are editable (the rest are not.
Thanks!