Which of the Following Is NOT an Example of a Microaggression

Which of the following is NOT an example of a microaggression against an out-group

A)  A white person provides friendlier service to white customers than to black customers. 
B)  A white person will not sit on the bus next to a black individual. 
C)  A man assumes a woman cannot do math. 
D)  A man is courteous to a woman on the bus who is carrying multiple packages and attempting to hold on to her child's hand.