The correct answer is <span>the values are measures for the sampling distribution of the mean
For example, in the </span>μm it is used to<span> represent the mean of the distribution of sample </span>means, while in the σm it is indicated that this value is a standard deviation, and just the M means that it is the standard deviation for the distribution of sample <span>means</span>
I would say b. precious stones Example of commodities that have been used as mediums of exchange include gold, silver, copper, salt, peppercorns, tea, large stones (such as Rai stones), decorated belts, shells, alcohol, cigarettes, cannabis, candy, cocoa beans, cowries and barley.
Declaration of Independence
If I'm not wrong it's electric because without electricity many advancements wouldn't have been possible like for example; trains, light, radio etc; hoped it helped!