Make a Python program using IE$-2-4($counter with 'while' loop$)$

A user enters a sentence. And then the user enters an alphabet.

Sort the words only with the alphabet $($both upper and lower cases$)$

Use only one "while" statement, and use upper$()$ and lower$()$ string m

Start with below

$a=$ input$(\text{'}$Enter a sentence: $\text{'})$

$b=$ a$.$split$()$

c $=$ input$("$Enter an alphabet: $")$