Final answer:
Big states have indeed achieved proportional representation in the lower house, as their representation aligns with the population, fulfilling the principles of proportional representation systems. The correct option is A.
Step-by-step explanation:
The question relates to the electoral system within a legislative body, specifically focusing on how big states achieve representation in the lower house.
Based on the information provided, which references the proportional representation systems and the seat allocation in the lower house based on population, the correct statement regarding the situation is: Big states have achieved proportional representation in the lower house.
This is confirmed by the description of the lower house's seat allocations, which states that in countries like Brazil, more populous regions receive more representation, aligning with the principle of proportional representation.