Answer: d. venom
Step-by-step explanation:
The copperhead and the rattlesnakes are both pit viper snakes that means they detect the minute differences in temperature by sensing the heat through their eyes and nostrils. Thus these snakes accurately detects the sense of heat of a particular prey. Their venom is a potent toxic which can kill a prey in single bite.
Therefore, because of the presence of deadly venom present in them these snakes exhibit very few natural predators.