In an agricultural experiment, the effects of two fertilizers on the production of oranges were measured. Fourteen randomly selected plots of land were treated with fertilizer A, and 10 randomly selected plots were treated with fertilizer B. The number of pounds of fruit was measured from each plot. Following are the results. Fertilizer A

409 443 369 396 421 410 458

420 413 402 400 429 418 401

Fertilizer B

399 543 327 363 391

517 384 350 448 386

Assume that the populations are approximately normal. Construct a 99% confidence interval for the difference between the mean yields for the two types of fertilizer.

a. (-33.5, 75.9)

b. (-28.1, 70.9)

c. (-19.5, 62.0)

d. (-23.5, 66.0)