In January 2009, the Green Power Partnership (GPP, sponsored by the EPA) listed Northwestern as one of the top 10 universities in the country in purchasing energy from renewable sources. The university matches 74 million kilowatt hours (kWh) of its annual energy use with Green-e Certified Renewable Energy Certificates (RECs). This green power commitment represents 30 percent of the university's total annual electricity use and places Northwestern in the EPA's Green Power Leadership Club. The 2010 Report by The Sustainable Endowments Institute awarded Northwestern a "B-" on its College Sustainability Report Card. The Initiative for Sustainability and Energy at Northwestern (ISEN), supporting research, teaching and outreach in these themes, was launched in 2008.
 What grade was given to Northwestern on the 2011 College Sustainability Report Card by The Sustainable Endowments Institute?