O resultado da execução desse script é:

Gabarito: D
The match() method searches a string for a match against a regular expression, and returns the matches, as an Array object.
Note: If the regular expression does not include the g modifier (to perform a global search), the match() method will return only the first match in the string.

This method returns null if no match is found.

Perform a global, case-insensitive search for "ain":

var str = "The rain in SPAIN stays mainly in the plain"; 
var res = str.match(/ain/gi);

The result of res will be:

ain,AIN,ain,ain

http://www.w3schools.com/jsref/jsref_match.asp