how can a custom content filter be added in wordpress

How can a custom content filter be added?

Use the right option from the following

  1. by using add_action(‘the_content’,’my_custom_filter’)
  2. by using add_filter(‘the_content’,’my_custom_filter’)
  3. by using wp_filter(‘the_content’,’my_custom_filter’)
  4. by using add_action(‘content’,’my_custom_filter’)

The right answer:

by using add_filter(‘the_content’,’my_custom_filter’)