Final answer:
The statement that best aligns with death penalty advocates' belief in its deterrent effect is that studies show a decrease in homicide rates in states with the death penalty, despite research often not supporting this.
Step-by-step explanation:
The statement that best supports the claim that capital punishment can be an effective deterrent is c) Studies show a decrease in homicide rates in states with the death penalty. Advocates for the death penalty argue that it serves as a severe punishment and the possibility of facing this ultimate penalty acts as a deterrent to potential offenders. This point of view relies on the assumption that a direct link exists between the presence of capital punishment and a consequential decrease in homicide rates. However, it's important to note that research and statistics have often not supported this assumption. Critics highlight the lack of consistent evidence for the death penalty's efficacy as a deterrent and point out issues such as wrongful executions and the potential for bias. It is a deeply complex and ethically charged topic with passionate arguments on both sides.