1. What sorts of transformations and differencing are needed to make the Cement series from aus_production stationary? Do the tests agree with your decisions?

2. Generate the a10 and the h02 series from the PBS tsibble we explored earlier using the code below.

   a10 <- PBS |>
     filter(ATC2 == "A10") |>
     summarise(Cost = sum(Cost))
   
   h02 <- PBS |>
     filter(ATC2 == "H02") |>
     summarise(Cost = sum(Cost))

   What are the features of these series in terms of stationarity and what operations do you need to take to turn them into stationary series.

3. Explore the the Algerian exports series from the global_economy tsibble. Is the series stationary? Is the series white noise?