Final answer:
The best concrete curing method is moist conditions for 7 days at 50 degrees, as it provides sufficient hydration without causing cracking.
Step-by-step explanation:
The best method for curing concrete is to keep it in moist conditions for an extended period which allows for proper hydration of the cement, thereby increasing the strength and durability of the concrete. Among the options provided, the ideal condition would be option 4: Moist condition for 7 days at 50 degrees. Although higher temperatures can accelerate strength gain, temperatures that are too high can lead to uneven curing and potential cracking. Moreover, extended moist curing times are beneficial for strength development, making option 4 the best among the given choices.