Please answer a question about the following article about Somerset:

Hinkley Point C nuclear power station is a project to construct a 3,200 MW two reactor nuclear power station. On 18 October 2010, the British government announced that Hinkley Point already the site of the disused Hinkley Point A and the still operational Hinkley Point B power stations was one of the eight sites it considered suitable for future nuclear power stations. NNB Generation Company, a subsidiary of EDF, submitted an application for development consent to the Infrastructure Planning Commission on 31 October 2011. A protest group, Stop Hinkley, was formed to campaign for the closure of Hinkley Point B and oppose any expansion at the Hinkley Point site. In December 2013, the European Commission opened an investigation to assess whether the project breaks state-aid rules. On 8 October 2014 it was announced that the European Commission has approved the project, with an overwhelming majority and only four commissioners voting against the decision.

What did the European Commission review
opened an investigation to assess whether the project breaks state-aid rules