This candidate not only chose good data, but she explored reasons why the time series showed an unusual pattern in some years. She writes:

"There is still something that’s bugging me with our data. The original series and the transform series have a strange behaviour. From the original series, the price goes down from 1995 to 2000 and after goes up until 2003 and crash. The transform series indicate large volatility from 1995 to 2000. There is a big variation in the middle of 2003 and stabilized after. What happen in that industry over the last 15 years, why the price of a kilogram of round steak goes up and down like that. We’ve been eating meet for as long the human kind exists; the price is not supposed to be that volatile. We are not in an abnormal inflation era. After a few moment of deep thinking, I found it!. My answer is on the next page."

Her answer seems correct, and it shows how exogenous effects influence the time series.