What is one reason steinbeck uses parallelism in the grapes of wrath

What would lead a historian to consider two events to have a relationship of correlation rather than causation?

Why did anne frank feel that the germans were the enemy?

Which suggests the most critical aspect of the peak oil theory? 1) controversy rages over rumors that the fracking lobby in washington has influenced the statistics. 2) supporters and critics argue endlessly over the rate of extraction and shape of the bell curve. 3) saudi arabia will soon have to begin fracking, leading to protests and further destabilization. 4) a new oil discovery means a fresh peak cycle, making that region the target of aggressors.