Click the Exhibit button.  From a local machine， connectivity with a server named server1.comptia.org is checked. It cannot be reached， but it can  be accessed via the IP address.   Which of the following is the MOST common cause of this error？（）    

• A、 The server is down.
• B、 The DNS server is down.
• C、 The local DNS cache is full.
• D、 The local DNS client is stopped.
• E、 The local DNS cache is corrupted.