They first sun-dried the leather for two to three days to make it rigid and tough.

A. The leather was first sun-dried to make it rigid and tough for two to three days.
B. To make it rigid and tough, the leather had been first sun-dried for two to three days.
C. The leather was first sun-dried for two to three days to make it rigid and tough.
D. The leather had been first sun-dried for two to three days to be made rigid and tough.