New Delhi, June 20 : Bollywood superstar Shahrukh Khan has showered praises on his "RA.One" co-star Kareena Kapoor for her hard work and sincerity in completing the shooting in time."Finished the last few bits and pieces of 'RA.One' with Kareena. Want to thank her for working so hard and fast...she was such a sport. Hope we haven't tanned her too much in the hot sun," Shah Rukh posted on his