How to Access list item in workflow task form

Hello all,

i am new so do not know very much. please help.

i have developed a workflow and custom aspx task form from visual studio 2012. i have access to task  items .

how i can access list item on which workflow was started. in task form code behind. ????

i have custom content type and some columns in it. while creating task how it is posible to assign that custom column of custom content type to a value from SPD 2013 or Visual studio single task activity .

Thanks in Advance.

Mukesh