Which of the Following Would Increase GDP

Which of the following would increase GDP?  

A)  More people walk to work rather than drive cars. 
B)  Consumers in rural areas switch from buying home heating oil to burning wood collected from their own land. 
C)  Farm families grow more for themselves than for the market. 
D)  The amount consumers spend on buying new vacuum cleaners does NOT change, but the quality of vacuum cleaners decreases so much that consumers spend more on repairing them.