Step 1: Analyze the sentence.
The sentence talks about an event that happened in the past (the 1970s). Therefore, we need to use the past tense.
Step 2: Evaluate the options.
(a) "are required to submit" is in the present tense, which is incorrect for describing a past event.
(b) "were required to submit" is in the past tense, which is appropriate for the 1970s, as the action occurred in the past.
(c) "required for submission" is grammatically incorrect and does not fit the structure of the sentence.
(d) "requirement of submitting" is awkward and does not correctly convey the meaning in the context of the sentence.
Step 3: Final Answer
The correct answer is (b) were required to submit.
Final Answer: The correct answer is (b) were required to submit.