I used [‘Engine size’, ‘Cylinders’, ‘City’, ‘Highway’, ‘Combined’,
‘Combined (mpg)’, ‘CO2 emissions’]
The grader feedback unclear to me:
Failed test case: You have some extra features in your list of numeric_features.
Failed test case: correlation_matrix has an incorrect value. Please check your correlation matrix.
Hello, @Lam_Chou_Vun_Dennis,
Please check out the extra hint above the cell by clicking on it and it will expand.
While it has explained it, I want to add that we don’t just consider a feature populated with numbers as numeric feature, because ordinal feature and categorical feature may also be numbers. For categorical, it is super clear because its values don’t have to preserve any meaning of ordering. 
For ex 3, try again after passing ex 2 because the former depends on the latter.
Cheers,
Raymond
OK all done.