A customer is using DSL to connect to the internet. After adding a new phone extension, the customer can no longer access the internet. Which of the following should be checked FIRST?

A.
Whether the ringer equivalency number (REN) has been exceeded.

B.
Whether the extension cable is DSL-capable.

C.
Whether the router developed a fault.

D.
Whether the new extension is connected to a DSL-filter.