Identify a lurking variable in a given situation

Stephanie knows that a correlation between the number of bars and the number of churches in her city does not, in itself, mean that more bars will lead to a higher number of churches.

Which of the following would NOT be a lurking variable in the above scenario?

• a.) The day of the weekthat Stephanie attends service
• b.) The city's budget
• c.) Population density
• d.) Stephanie's proximity to the center of the city