SPECIAL STEP: Remove the first column from concrete_df, "OBS#", as it's not a valid predictor. Display the names of the remaining columns. Your output should look like this: Index(['Manufacturer', 'Cement', 'Blast_Furnace_Slag', 'Fly_Ash', 'Water', 'Superplasticizer', 'Coarse_Aggregate', 'Fine_Aggregate', 'Age', 'Comp_strength'], dtype='object') In [ ]: ### ### YOUR CODE HERE