Replication of Circular DNA Occurs at the "Bubbles" or "Eyes",also $\theta$

Replication of circular DNA occurs at the "bubbles" or "eyes",also called ______ .

A) " $\theta$ structures"
B) " $\phi$ bubbles"
C) " $\theta$ bubbles"
D) " $\sigma$ structures"
E) " $\sigma$ bubbles"