Falak lists the four events involved in the formation of sinkholes.W - Acidic rainwater dissolves the limestone bedrock.X - Large cavities form in the bedrock.Y - Natural holes and cracks become bigger.Z - The ceiling collapses due to the weight of sediment.

Acidic rainwater first dissolves the limestone bedrock (W). This widens natural holes and cracks (Y), allowing larger cavities to form (X). When the cavity ceiling can no longer support the sediment above it, it collapses (Z). So the correct choice is B, W, Y, X, Z.

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