Letters, anyone?

I have a little game for you today. Anyone can participate. Just guess a letter or two of what you think might fit into the following phrase. It's actually a new quote I happened across and really like.

So, just leave a comment with a letter and I'll fill in the blanks. I'll continue to update this post as I receive your guesses!

a     book    that    is    shut,    is    but    a    block.

16 letters guessed: A, B, C, D, E, F, H, I, K, L, N, O, S, T, R, U