Answer: C) a general rule most people follow
The english phrase "rule of thumb" referes to an approximate method for doing something, based on practical experience rather than theory. An example of a rule of thumb would be: changing the oil of a car every certain number of milles traveled. "To start with, change the oil every 5000 or 6000 miles". In the example you can notice that is not strictly accurate or reliable for every situation.
