3. In the following real-world data (Iphone) tuples with missing values for some attributes are a common occurrence. 1 iPhone iPad Mac iPod 25 NA NA 1,3 1,6 26 27 28 Quarter Q2 2006 Q3 2006 Q4 2006 Q1 2007 Q2 2007 Q3 2007 Q4 2007 Q1 2008 Q2 2008 Q3 2008 N/A N/A 29 N/A N/A N/A N/A 1,1 N/A 2,3 N/A 1,7 N/A 0,7 N/A 6,9 N/A 30 8,1 8,7 21 10,5 9,9 10,2 22,1 10,6 11 11 1,6 1,5 1,7 2,2 2,3 2,3 2,5 2,6 31 32 33 34 What is the output for the following commands for the Iphone dataframe a). Iphone. dropna (2M) b). Iphone dropna (axis='column, thresh=4) (2M) b). Iphone dropna(axis="rows) (2M) c). Iphone dropna(axis="column", how=all) (2M) d). Iphone fillna(method=bfill', axis=1) (2M)