Sorry, kevin, I made a wrong spelling: "Associate" to "Assistant", thought they are synonymous.
This is the first level certification of the Oracle DBA. Two exams needed: PL/SQL and Database Fundamentals I. I think OCA is enough for me as a developer. The tests helped me a lot to learn the basic knowledge of Oracle Database.
I also confuse about that two listener.
I was lucky to pass the exam. I will do some tests about it. see you.