Compute the probability of the following two sentences:

S1: Sales of the company to return to normalcy. S2: The new products and services contributed to increase revenue.

Using the trigram language model trained on the corpus that is provided, find out which of the two sentences is more probable. Compute the probability of each of the two sentences under the following two scenarios: a) Use the trigram model without smoothing. b) Use the trigram model with add-one (Laplace) smoothing. c) Use the trigram model with Katz back-off smoothing