Answer:
I) Sexual reproduction
II) Mutation
Explanation:
Variations refer to the difference observed within organisms of the same species. Variation are introduced into a population by:
- new genetic combinations that occur during sexual reproduction (i.e during meiosis)
- mutations, spontaneous changes that occur in genes and chromosomes.
The U.S. has one of the highest, if not, the highest obesity rate in the world.
D - an increase in tree cover in the tundra.