一道SAT2物理题,Q:When a woman pushes on her grocery cart,the woma

一道SAT2物理题,
Q:When a woman pushes on her grocery cart,the woman moves because of ()
the answer is the force that the ground exerts on the woman.
In light of the net force,the woman horizontally gets the opposite reaction from the cart and the friction of the ground.
I really wonder which one is the main factor.
PS:In the question,it does't tell me anything about frictional coefficient,thus I think there is friction on the ground by default.
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