user
One by one we come to life and side by side we wait, while our company swells in number some come early some come late.  Some will bore you, some enthrill, but you can not choose between us, you must take us one and all, because we're bound together tightly and we're naught if we break free; if you want some clues about us simply answer who are we?
A: faithful
B: bookmaker
C: summons
D: chapters
E: learning
assistant
<|begin_of_thought|>

Deep Thought is thinking for 7.5 million years.

<|end_of_thought|>

<|begin_of_solution|>

D

<|end_of_solution|>