A researcher is comparing three new formulas for grass killer. To conduct the experiment, the researcher purchases 30 pieces of sod from various vendors to use in the study. To create the three treatment groups, the researcher numbers the pieces of sod 1–30 and places the numbers in a hat. The researcher randomly selects 10 numbers, making sure to mix the numbers between each selection, and then repeats that process one more time to select the pieces of sod in the experiment. Which component is missing from the researcher’s process?

The researcher did not use randomization when assigning the groups.
The researcher should not have purchased sod from different vendors.
The researcher did not assign the chosen pieces of sod to treatment groups.
The researcher should have randomly selected 10 numbers a total of three times.