I believe it is B. Hope this helps!!
A useful index fossil must be distinctive or easily recognizable, abundant, and have a wide geographic distribution and a short range through time.
The answer in the space provided is the preserved bacteria. It is because most foods are chilled in order to prevent the food from spoiling but in the same time, the bacteria that resides in the food, especially in meat products, are being preserved. In order for it to be killed, it is best to cook it thoroughly and properly, in order for the bacteria to be killed and safe for the people to consume.
