<input type="checkbox" id="set_1" checked> click to show text1
<p class = "wpbook_hidden wpbook_option_set_1"> This is option one</p>
<p class = "wpbook_hidden wpbook_option_set_1"> This is another option one</p>
<input type="checkbox" id="set_2"> click to show text1
<p class = "wpbook_hidden wpbook_option_set_2"> This is option two</p>