Granite Insurance Company entered into a treaty reinsurance agreement with Rock Solid Reinsurance $($RSR$).$ Granite's retention limit is $$400,000$ and RSR agreed to provide reinsurance for up to $$2\mathrm{.}0$ million. If Granite writes an $$800,000$ policy, RSR is responsible for $50$ percent of the losses. If Granite insures a $$1\mathrm{.}6$ million risk, RSR is responsible for $75$ percent of any losses. What type of reinsurance arrangement did Granite enter into with RSR$?$

A$)$ reinsurance pool

B$)$ surplus share reinsurance

C$)$ facultative reinsurance

D$)$ excess of loss reinsurance