Greta Thunberg is a well-known environmental activist who comes from Sweden, which is why option 1 is the correct answer. Greta gained international attention for her strong and vocal stand on global warming and climate change.

In the other options: 2- Germany, 3-USA, and 4- Canada; these are all countries with their own notable personalities and contributions in different domains, including environmental activism. However, in the context of this particular question, none of these countries are correct because Greta Thunberg is not from Germany, USA, or Canada, but Sweden.

So, to reiterate, Greta Thunberg is a Swedish environmental activist making option 1: Sweden the correct answer to the question of her nationality.