First, make the 3 radio buttons have the same name, but with different Export values, such as Option1, Option2, Option3.
Next, have all the fields in Section A named beginning with "SectionA.", such as SectionA.field1, SectionA.field2, SectionA.field3, etc.
Then use this script as the mouse up action for the radio buttons:
if (event.target.value!="Option1") { //If Option1 radiobutton is on, lock Section A
this.getField("SectionA").readonly = false
}
else this.getField("SectionA").readonly = true //Otherwise, unlock them