How do NEC4 Options A to E differ on payment?

The main option decides what the Price for Work Done to Date is, and everything else follows from that. Option A is a priced contract with an activity schedule: the Contractor is paid the Prices of completed activities, nothing for partly completed ones, and it carries the cost risk within each activity. Option B is a priced contract with a bill of quantities: the Contractor is paid the measured quantity of each item at the bill rate, plus completed proportions of lump sums, so quantity risk is shared through remeasurement while rate risk stays with the Contractor. Under both, Defined Cost matters only for assessing compensation events. Option C is a target contract with an activity schedule and Option D a target contract with a bill of quantities: the Contractor is paid the Defined Cost the Project Manager forecasts will have been paid before the next assessment date plus the Fee, the activity schedule or bill sets the total of the Prices as the target, compensation events move the target, and at Completion and in the final assessment the difference between the target and the Price for Work Done to Date is shared under clause 54. Option E is cost reimbursable: Defined Cost plus Fee, with no target and no share, so the Client carries the cost risk. Option F, the management contract, also pays on cost but is rarely met. The records burden rises from A to E: proof of completion under A, measurement under B, and accounts and records for every component under C, D and E, because unjustified cost is Disallowed Cost. What goes wrong: Contractors on Option C treat the target as the price; Option A activity schedules are drafted for tender comparison rather than cash flow; Option B bills contain errors nobody corrects; and Clients choose a cost option without the staff to audit the cost.