Final answer:
The number of people estimated to be victims of workplace violence every year is not provided in the given information.
Step-by-step explanation:
According to the information provided, every year there are nearly two million workers in the US who are physically assaulted or threatened with assault in the workplace. However, it does not specify how many of them are victims of workplace violence. Therefore, none of the given options (a. 500,000, b. 750,000, c. 2,000,000, d. 2,750,000) can be considered as a correct estimate based solely on the given information.