Answer:
That unanswered question became both an oppressive shroud over Klaus's childhood and a sinister playmate, as he often let his mind to wander, imagining horrors or enemies that must have been so great that only such a great, grey, stone wall could keep them out.
Explanation:
The above sentence best communicates the author's message that the Berlin Wall made citizens feel afraid.
This is true because we discover from the text that the issue of the wall making Klaus afraid was an oppressive shroud over his childhood. It made his mind to wander and to imagine horrors.
This reveals that Klaus's fear which started from his childhood would have been shaped by what the other citizens told him about the wall. If he as a citizen feels this way, it shows that others will feel same as well.
