Question

when geologists are using the principle of lateral continuity, they think of different things that could have separated the rock strata, ________ erosion from a river or tectonic plate movement. a such as b even though c in closing d at last

Explanation:

"Such as" is used to introduce examples. Here, "erosion from a river or tectonic plate movement" are examples of things that could separate rock strata. "Even though" is for contrast, "in closing" is for ending a speech - like context, and "at last" is for indicating a final event in a sequence. None of those fit the context of giving examples.

Answer:

A. such as