Professional service and construction administration contracts commonly include safety-related clauses that allow the professional to suspend services or treat the contract as discharged/terminated where unsafe conditions exist. NPPE materials emphasize that the duty to the public (including worker safety) is paramount, and professionals must not continue work in circumstances that create unacceptable risk. Accordingly, contracts often recognize that if site conditions are unsafe—or if the professional is prevented from performing duties safely—the professional may stop work, require corrective action, and potentially terminate the agreement. The other items (A, D) relate mainly to payment disputes among owner/contractor/sub-trades and are typically addressed through payment certification mechanisms, lien processes, or contractual remedies between those parties, not as a standard “professional discharge” trigger. Non-compliance with contract requirements (C) can lead to remedies, notices, and potential termination, but the classic and most directly recognized discharge/suspension trigger for a professional is unsafe working conditions given the overriding safety duty. Therefore, B is best.