In this case, we'll have to carry out several steps to find the solution. 
Step 01:
Data
Diagram
secant = ?
Step 02:
We must analyze the diagra,m to find the solution. 
Secant ===> straight line that cuts a curve in two or more parts 
Segments:
CD: FALSE
AB: FALSE
AO: FALSE
BC: TRUE 
The answer is: 
Segment BC is a secant