Jacy wants to determine how age and height are related to shoe preference in her town. She selects a simple random sample of 25 individuals taller than five feet seven inches from the 18- to 21-year age group and records their age, height, and shoe preference (tennis shoes, high-heeled shoes, sandals). She also selects an independent simple random sample of 30 individuals shorter than five feet seven inches from the 35- to 45-year age group and records the same information. Which is themostimportant observation about Jacy's plan?

Her samples are too small.

She should have used equal sample sizes.

The plan is well conceived and should serve the intended purpose.

She will be unable to tell whether a difference in shoe preference is related to a difference in age or to a difference in height.

She should have selected the two age groups randomly instead of choosing them specifically.