I don't know whether this was one of your options, but South Asia can be very well characterized as a Sub-continent.
In fact, it's is commonly referred to as "the Indian Subcontinent" or even simply "Subcontinent". One of the reason for a distinction of this part of the land is that it lies on a different tectonic plate.
<span />
I believe it runs north & south, to my understanding odd numbers runs N & S,
while even numbers runs E & W.
Answer:
a. They must be present in a large geographic area.
Explanation:
Index fossils can be used to determine the age of a rock strata with great precision, but they must be scattered over a large geographic area to be able to be used reliable for this type of measurement. Index fossils typically indicate a certain type of paleoenvironment belonging to a very specific prehistoric period and their formation coincides with the age of the rock layer.
