Answer:
natural polymers and manufactured polymers.
Explanation:
In an experiment testing the effects of a treatment, a comparison grouprefers to a group of units (e.g., persons, classrooms) that receive either no TREATMENT or an alternative treatment.
Stefan Löfven, now Prime Minister of Sweeden, studied social work at Umeå University, but dropped out after a year and a half.
Then, he started a welding course and after Military service, he began his career as a welder and he started getting into unions and politics.