In this July, 12 2011 photo, Caterpillar excavators tear down Martin Luther King, Jr. Senior High School in Detroit. Continued robust demand for Caterpillar's heavy equipment boosted the company's second-quarter profits by 44 percent, but higher costs and cautious comments about China's economy sent shares sliding Friday, July 22, 2011. (AP Photo/Paul Sancya) Photo: Paul Sancya, ASSOCIATED PRESS / AP2011