HELP I know the answer isn't A because I put it last time and it was wrong

What is the “narrow cell” in line 15 of “elegy written in a country churchyard”

One of the author's purposes in the code book is to explain different types of codebreaking to his readers. which line best demonstrates this purpose? a theoretical breakthrough would be a fundamentally new way of finding alice's private key mathematicians have been studying factoring for centuries, and modern factoring techniques are not significantly better than ancient techniques a more recent development is the so-called tempest attack, which aims to detect the electromagnetic signals emitted in a computer's display unit if scientists could build a quantum computer, it would be able to perform calculations with enormous speed mark this and return save and exit next submit

Best one will be the brainiest ! what is the summary of the book open window by saki?