Which of the following most logically completes the passage?

The Roman emperors issued coins made of a silver-copper alloy. Over time the silver content in the alloy used for minting was reduced from an original 90% to less than 10%. The coins, however, continued to appear silver on the outside. It is therefore tempting to suspect that the silver surfaces were added to hide the reduction in silver content. However, that suspicion is probably groundless, since ______.

surviving late Roman coins that are much worn often do not appear silver at all

the Roman emperors were increasingly unable to afford to maintain a high silver content in their coins

in Roman times it would not have been possible to analyze the exact proportions of the metals in a coin once it had been minted

most members of the public were probably unaware of what the coins looked like inside 

Roman metalworking methods of the time would have naturally resulted in a layer on the surface of any silver-copper alloy


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