how do i Insert into different tables of db according to option selected in dropdown list using php pdo please help me

I have 5 different table. e.g. mechanical,civil,chemical,petroleum and elect. i want a page with name and dropdown option in php. so, according to the selected dropdown option the name should be inserted to the associate table in db. eg. if i give any name mechanical and select mechanical option. then the name sholud be inserted in mechanical table.
here is my code