Answer:
I think 4) the focus is the answer
The economies of the United States and Canada have had a very similar development over their recent history.
Both started by being places where the agriculture and fur trade were the basis of the economy, so they were in general engaged into the primary economic sector.
Once the industrialization was introduced, the countries very quickly switched to the secondary economic sector by becoming heavily industrialized and instead of selling raw materials and products, they were manufacturing them.
As they were becoming more developed and wealthier, they had a big advantage over most of the countries in the world, so they were able to start to engage in the tertiary and quaternary economic sectors, which have became the leading economic sectors in the modern times.
Because the toxins from gas are not good to breath in and eventually we will al die from it
