PITTSBURGH (AP) — Shell Oil Co. has chosen a site near Pittsburgh for a major, multi-billion-dollar petrochemical refinery that could create thousands of construction jobs and provide a huge economic boost to the region. Dan Carlson, Shell's General Manager of New Business Development, said Thursday that the company signed a land option agreement with Horsehead Corp. to evaluate a site near Monaca, about 35 miles northwest of Pittsburgh. The so-called ethane cracking, or cracker, plant would convert ethane from bountiful Marcellus Shale natural gas liquids into more profitable chemicals such as ethylene, which are then used to produce everything from...