Drupal How to add the dropdown in the search box

by default we have drupal search box,

i want to add one dro开发者_运维知识库pdown , that should contain the content types(like page,story,article)

i know there is a lot of modules, but i want to know, using hook module, i want to add the

dropdown,

i want to do it with only hook methodm

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Try providing a preprocess for the search form function in your theme's template.php file. There's a nice example of it here.