The diagram below shows several rock layers and other geologic features. Each feature is labeled with a unique letter. The order of the letters do not necessarily reflect the order in which the features formed. Examine the diagram, and answer the question that follows.


Using the principles of original horizontality, superposition, and cross-cutting relationships, determine the missing step in the following order of events:
The lower layers were originally deposited as horizontal layers in the following order: M, N, P, Q, R.
___?___
Igneous intrusion G cross-cut layers M–Q.
Erosion occurred at surface X (unconformity).
The upper layers were deposited in the following order: H, I, J.
Alternatively, igneous intrusion G may have cross-cut layers M–Q before the layers were tilted or even before layer R was deposited.
A.
Layers M–R were tilted.
B.
Erosion occurred in layer J.
C.
Erosion occurred in layer I.
D.
Layers H–J were tilted.