Why were political machines difficult to break up?
they always operated within the law.

they created a cycle of supply and demand.

they used violence to intimidate voters.

they created a cycle of favors for votes.

It's they created a cycle of favors for votes and they used violence to intimidate voters.

D. They created a cycle of favors for votes

Explanation:

right on ed2020

the invasive species was introduced due to commercial purpouses, as there was a demand for fur clothes and hence, a business opportunity connected to this product. actually, it was when the nutrias scaped, causing harm to the us ecosystems when they acquired the status of invasive species. in this case they have caused an environmental problem, but it could have affected also economic interests or even human health.