Amendments issued before the established time and date for receipt of proposals must be sent to whom?

The correct choice is that amendments issued before the established time and date for receipt of proposals must be sent to all parties receiving the solicitation. This practice ensures fairness and transparency in the bidding process. By notifying all parties who received the original solicitation, it guarantees that everyone has access to the same updated information, which is essential for ensuring a level playing field among all potential bidders.

This comprehensive communication prevents any unfair advantages or disadvantages that could arise if only certain bidders received the amendments. It also upholds the integrity of the procurement process by ensuring that all interested parties can make informed decisions based on the latest information provided by the contracting agency.

In the context of the other options, only notifying all interested bidders would exclude parties who received the solicitation but did not express immediate interest in bidding. Limiting notifications to only those who submitted proposals creates an uneven distribution of information, which is not in line with best practices for transparency. Lastly, the idea that no one should be notified if unrequested is counterproductive, as it risks undermining the integrity of the solicitation process, allowing for confusion and potential complaints from bidders who might have benefitted from the additional information.