Tiger cub

The tiger Tishka really wants
Read all the books in the world.
He looks serious -
Studying the alphabet.
Letters will appear in order
If you ask a riddle:
A, B, C, D, D, E, E
She has three ears.
F, Z, I, Y, K, L, M
There are no legs and belly at all.
H, O, P, R, S, T, U
Its tail is about a mile long.
F, X, Ts, Ch, Sh plus Sh
She has a hole in her cloak
B, s, b
There is no way to catch her.
And in addition E, Yu, I -
I invented it myself,
And I'll tell you a secret
There is no answer to the riddle!