What happens when additional object tokens arrive at an input pin?

When additional object tokens arrive at an input pin, they must wait for the activity to complete. This behavior is intrinsic to how activities manage their input pins in a modeling context, particularly within the realm of object-oriented design and execution semantics.

In typical modeling scenarios, an input pin can only process a limited number of tokens at a time. The processing of these tokens is sequential, meaning that an activity must finish its current execution before it can accept and process new tokens arriving at its input pins. This ensures that the activity's internal logic remains consistent and that it doesn't try to process multiple inputs simultaneously in an undefined manner.

This model of operation helps maintain the integrity of the process flow and avoids potential conflicts that might arise from simultaneous handling of inputs. Therefore, the correct answer highlights an essential aspect of model execution regarding the handling of input tokens, ensuring orderly processing and adherence to defined behavior.