<prompt> Closure of the foramen primum results from fusion of which of the following structures?Septum secundum and the fused atrioventricular cushionsSeptum secundum and the septum primumSeptum primum and the fused atrioventricular cushionsSeptum primum and the septum spurium  <response>: C. The foramen primum forms between the free edge of the septum primum and the atrioventricular AV cushions. It is closed when the septum primum fuses with the AV cushions. 