``` s = pd.Series([1, 2]) df = pd.DataFrame([1, 2]) print(s.agg("sqrt")) print(df.agg("sqrt")) print(s.apply("sqrt")) print(df.apply("sqrt")) print(s.agg("size")) print(df.agg("size")) print(s.apply("size")) print(df.apply("size")) ``` In each of the two blocks, first three lines all give the expected output and the last raises.