MERCED, Calif. – First lady Michelle Obama praised graduating students at California's smallest, youngest public university for their determination to succeed, urging them to give back to their communities. In her debut as a commencement speaker on Saturday, Mrs. Obama evoked the struggles of California's founders — settlers and former slaves, trailblazers and immigrants — to encourage the 493 members of the school's first full graduating class to use their newfound skills to lift up those around them.