In September 2011 Helle Thorning Schmidt has been elected as the Prime Minister of

Denmark
Finland
Norway
Sweden

The correct answer is (a). Helle Thorning-Schmidt was elected as the Prime Minister of Denmark in September 2011. She was the first woman to hold this position. She served as Prime Minister until June 2015.

(b) Finland: The current Prime Minister of Finland is Sanna Marin. She was elected in December 2019.

(c) Norway: The current Prime Minister of Norway is Jonas Gahr Støre. He was elected in October 2021.

(d) Sweden: The current Prime Minister of Sweden is Magdalena Andersson. She was elected in November 2021.