Both initial and final setting times
Ordinary Portland cement and rapid hardening cement have different characteristics, but they do share one common characteristic, which is the setting time.

Setting Time
The setting time of cement refers to the time taken by the cement paste to harden and gain strength after it is mixed with water. It is an important property of cement as it determines the workability and handling time of the cement during construction.

Initial Setting Time
The initial setting time is the time taken by the cement paste to change from a plastic state to a solid state. During this stage, the paste starts to lose its plasticity and becomes stiff. It is an indication that the cement is starting to set and cannot be remolded.

Final Setting Time
The final setting time is the time taken by the cement paste to completely harden and gain its full strength. At this stage, the paste becomes completely solid and can bear loads without deformation.

Comparison between Ordinary Portland Cement (OPC) and Rapid Hardening Cement (RHC)
Ordinary Portland cement and rapid hardening cement have different setting times.

- Ordinary Portland cement has a longer initial setting time compared to rapid hardening cement. It typically takes around 30 minutes to 2 hours for OPC to reach initial setting. This longer setting time allows for more workability and flexibility during construction.

- Rapid hardening cement, on the other hand, has a shorter initial setting time. It sets much faster than OPC, usually within 5 to 30 minutes. This quick setting time is advantageous in situations where rapid construction is required.

However, despite the differences in initial setting time, both OPC and RHC have the same final setting time. The final setting time for both types of cement is typically around 24 hours. This means that both OPC and RHC will reach their maximum strength and hardness after 24 hours of setting.

Therefore, the correct answer is option 'C' - Both initial and final setting times.