Let's deconstruct the sentence :
1. "Because of the enormous research and development expenditures required to survive in the electronics industry" (an adverbial clause)
2. "an industry marked by rapid innovation and volatile demand"(appositive for electronics industry)
3. "such (a modifier/qualifier for "firms", the subject of the sentence) firms tend to be very large".
Does the subject - "such firms" - refer to any firms mentioned before ? No, so we need to include that.
(B) is the answer.
"Education is what remains when one has forgotten everything he learned in school."