A researcher is testing the effects of plant food on plant growth. 9 plants have been given the plant food. Another 9 plants have not been given the plant food. The heights of the plants are recorded after 8 weeks. The populations have normal distributions. The following table is the result. The researcher thinks the food makes the plants grow taller. Plant Group Sample Mean Height of Plants (inches) Population Standard Deviation Food 16 No food 14 2.5 1.5 6 11 PRO a. Is the population standard deviation "known" or "unknown"? Enter one of the preceding options without quotes b. What is the p-value? If your answer is less than .01, enter 0. c. At the 1% significance level, do we reject the null hypothesis? OA. Yes OB. No Submit answer