p

The prefix 'im-' is often used in front of words that begin with 'm', 'p', or 'b', making words like 'immature' or 'impossible'.

Sometimes we do write things that we can't pronounce, like these: you can't hold the letter p for that long, or this where all those letter Es are silent!

They're going to be attacks on the most fundamental and important questions of the day, whether it's the Riemann hypothesis, Navier-Stokes or P versus NP, just to pick a few.

If you say some of the letters you recognise off the top row, as you move left to right, you can feel those letters moving backwards in your mouth: p, t, k.