Answer:
Correct answer is b(Through friction between her feet and the carpet)
Step-by-step explanation:
Whenever we rub our body against carpet or any other object made of fiber materials that time frictional force act. Due to frictional force our body get some extra electron.
When Tracy scuff her feet across a carpet, That time due to friction between her feet and carpet she got some extra electrons. These Electrons can move easily through conductor. When Tracy touched the doorknob which is made up of some metal(conductor) and has positive charge that time extra electrons moved from Tracy to the knob. Due to quick movement of electrons Tracy gets a small shock.