Final answer:
For requirements exceeding the micro-purchase threshold, contracting by negotiation is the most appropriate method of purchase, offering flexibility necessary for more complex acquisitions.
Step-by-step explanation:
The method of purchase most appropriate for requirements exceeding the micro-purchase threshold is c) Contracting by negotiation. Micro-purchases are small purchases a government agency can make without an elaborate contracting process. Once the micro-purchase threshold is exceeded, simpler methods can no longer be used. Simplified acquisition procedures might be ideal for small purchases that exceed the micro-purchase threshold but are still relatively low value and low complexity.
Sealed bidding, also known as formal advertising, is typically used when the government has very clearly defined requirements and expects that many companies could meet them, allowing for a competitive bidding process. However, contracting by negotiation is more suitable for complex purchases where terms and conditions might need to be discussed and negotiated with more flexibility, which often happens with acquisitions that exceed the micro-purchase amount.