In this tutorial, we'll learn about the methods in String class that help us to search and replace portions of the string based on a text or pattern.

• String.include?(string) - Returns true if str contains the given string or character. Very simple!

    > "hello".include? "lo"   #=> true  
    > "hello".include? "ol"   #=> false  

• String.gsub(pattern, <hash|replacement>) - Returns a new string with all the occurrences of the pattern substituted for the second argument: . The pattern is typically a Regexp, but a string can also be used.

    "hello".gsub(/[aeiou]/, '*')                  #=> "h*ll*"
    "hello".gsub(/([aeiou])/, '')             #=> "hll"

Either method will depend upon the problem you are trying to solve, and the nature of input-output behavior you desire.

In this challenge, your task is to write the following methods:

• mask_article which appends strike tags around certain words in a text. The method takes 2 arguments: A string and an array of words. It then replaces all the instances of words in the text with the modified version.
• A helper method strike, given one string, appends strike off HTML tags around it. The strike off HTML tag is <strike></strike>.

For example:

> strike("Meow!") # => "<strike>Meow!</strike>"
> strike("Foolan Barik") # => "<strike>Foolan Barik</strike>"
> mask_article("Hello World! This is crap!", ["crap"])
"Hello World! This is <strike>crap</strike>!"

Apply the helper method in completing your main method.