Final answer:
Various U.S. states have implemented all of the following voting reforms in conducting elections except for strict voter ID requirements.
Step-by-step explanation:
The voting reforms implemented by various U.S. states include early voting, same-day registration, and automatic voter registration. However, one reform that has not been implemented in some states is strict voter ID requirements. While some states have implemented such requirements, others have not made it mandatory for voters to show photo identification before voting. Therefore, the correct answer is c) Strict voter ID requirements.