Amateur gardeners who plant based on the phases of the moon tend to get better results than those who do not. This seems surprising since the phases of the moon do not affect how plants grow. An alternative practice often found among amateur gardeners is to plant during the first warm spell of spring, which leads to problems when a frost follows. So, amateur gardeners who use the phases of the moon are less likely to lose plants to a frost. The argument requires assuming which one of the following? ['Amateur gardeners who use the phases of the moon tend to plant different types of plants than do other amateur gardeners.', 'Amateur gardeners cannot improve their results unless they understand why their methods work as they do.', 'The phases of the moon affect whether a frost follows the first warm spell of spring.', 'Using the phases of the moon usually leads amateur gardeners to plant later in the spring than those planting at the first warm spell.']