Which statements about ISTM dropout are correct?

a$.$ ISTM needs special dropout techniques because a naive application of dropout will result in vanishing$/$exploding gradients.

b$.$ ISTM needs speciat fropout techniques because with a naive application the probability of a memory cell to "survive" decreases exponentially as the sequence grows in time.

c$.$ Dropout is a regularization technique that randomly sets activations to zero during the forward pass.

d$.$ It is especially important to apply dropout when evaluating the model.

e$.$ The central idea of zoneout $($Krueger et al$,2017)$ is to randomly clear the inputs $x(t)$ instead of the memory cell $c(t).$