Develop a JavaScript program with Ajax $($with HTML$/$CSS$)$ for:

a$.$ Use ajax$()$ method $($without Jquery$)$ to add the text content from the text file by sending ajax request.

b$.$ Use ajax$()$ method $($with Jquery$)$ to add the text content from the text file by sending ajax request.

c$.$ Illustrate the use of getJSON$()$ method in jQuery

d$.$ Illustrate the use of parseJSON$()$ method to display JSON values. kindly provide code and execution steps in ubuntu linux.