How to register a held down key.

Hello, I have the code below inside FixedUpdate

if (Input.GetKeyDown (KeyCode.D))
	print ("D key pressed");

but this does not work if ‘D’ is held down it runs once on each key press, and i’ve discovered that using a while loop freezes unity completely.
My question is how do I make the if statement run every frame if the ‘D’ key is held down?

Maybe what you’re looking for is Input.GetKey(). Also, I didn’t know about this method before a minute ago. That’s how long it took to look up the documentation.