For the following questions, the answers will have to do with the following four functions: $\backslash$textit$\{$get$$\backslash \_$$input$$\backslash \_$$gradients$()\},\backslash$textit$\{$get$$\backslash \_$$weight$$\backslash \_$$gradients$()\},\backslash$textit$\{$compose$$\backslash \_$$input$$\backslash \_$$gradients$()\},$ and $\backslash$textit$\{$compose$$\backslash \_$$weight$$\backslash \_$$gradients$()\}.$ Note that through the Diffable class, each of the layers shown a To initialize backpropagation, which function must you call on which layer? What partial derivative$($s$)$ would this return?