2 Points
What is an index fossil?
O
A. A fossil that contains rocks and minerals
O
B. A fossil found in rocks from one time period
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C. A fossil that has vestigial structures
O
D. A fossil that formed 300 million years ago

B, A fossil found in rocks from one time period

Explanation:

Fossils are used to determine the ages of rock layers. Index fossils are the most useful for this. Index fossils are of organisms that lived over a wide area. They lived for a fairly short period of time. An index fossil allows a scientist to determine the age of the rock it is in. Hope that this helps you :)

sorry, is there a picture? i do not see any arrows.

wut? unius0123 wut?

they had the law tat factories that produces smoke cannot be built near residential buildings.

building of proper sewage system was done to ensure that the waste is carried away from the humans so that they do not get diseases from it.

also they built water systems to provide water in those areas which are drought prone.