Çözüldü Sentence Structure - Grammar

Meetings and similar demonstrations, by themselves alone, can never attain the realization of great aims, _______ they can only have a healthy result if the spiritual power emanating from the nation's soul directly supports them.

A) why
B) when do
C) how
D) both
E) for

Correct Choice: E (for)

"The Great Speech" by Marshall Mustafa Kemal Atatürk

Explanation:
"For" meaning "because";
We sometimes use for as a conjunction meaning ‘because’. We use it in very formal, and often literary, contexts:
"Chasing the white stag through the forests, never catching it, of course, for it is a creature of legend."
https://dictionary.cambridge.org/grammar/british-grammar/for?q=for because