First Principles Thinking: numerical relation
C is correct. The required average balance equals total pool balance divided by number of loans. EUR 1,000,000,000 / 45,000 = EUR 22,222.22 repeating. Rounded to two decimals, that is EUR 22,222.22, so C is correct.
Why option A is incorrect. EUR 22,000 multiplied by 45,000 would produce only EUR 990 million, short of the target pool size.
Why option B is incorrect. EUR 22,200 multiplied by 45,000 would produce EUR 999 million, still below EUR 1,000 million.