. . . . . . . . specifies the function that will be called on an error event.

The correct answer is: A. callback

A callback function is a function that is called when a certain event occurs. In the context of the question, the callback function is called when an error event occurs.

The other options are incorrect because:

• B. error is not a function. It is a keyword that is used to specify that an error has occurred.
• C. connect is a function that is used to connect to a server.
• D. reconnect is a function that is used to reconnect to a server after a connection has been lost.

I hope this helps! Let me know if you have any other questions.