2. Since it’s developmental anatomy
        
             
        
        
        
I am pretty sure that the layer in figure 4-1 which forms the cap rock for the oil trap is the layer  F that shows an example of stratigraphic traps that includes unconformity, lens, pinch-out in which you can see how t<span>he oil is stuck inside the porosity of the rocks. 
Do hope you will find it helpful! Regards.</span>