At the time this exam was conducted, the dean of Harvard Business School was Nitin Nohria, who stepped into the role starting 1 July 2010. He had spent years teaching at HBS before being chosen as dean, and his appointment made him notable as the first person of Indian origin to lead the school.
Deepak Jain held a similar leadership post, but at a different institution altogether, Kellogg School of Management, so he does not fit here. Kim Clark had indeed once been dean of Harvard Business School, but his term ended in 2005 when he left to head Brigham Young University-Idaho, meaning he was no longer in the role by 2010. Since Nitin Nohria was actively serving as dean at the time of the exam, "None of these" cannot be correct either, leaving Nitin Nohria as the accurate answer.