The best response that describes Ruby gathering enough evidence to support a scientific explanation concerning plant growth rates is:
Ruby measures the heights of several species A, B, C, and D plants for a week under the same conditions and finds journal articles that describe the growth rates of each species.
This response indicates that Ruby is measuring multiple species under controlled conditions, which is essential for a fair comparison, and it also includes sourcing existing scientific literature to support her findings, thus providing a stronger basis for her conclusions.