Final answer:
The correct option is 'a. birthday.toDateString()'.
Step-by-step explanation:
The correct option to display the value of birthday in the document, formatted as Wed Feb 08 2017 is a. birthday.toDateString().
The toDateString() method returns the date portion of a Date object as a readable string. By calling this method on the birthday variable, we can display the value in the desired format.
Here's an example:
var birthday = new Date();
document.write(birthday.toDateString());