Which of the following is a complex sentence? a. central american economic problems force many workers to leave home. at the same time, u. s. job demands create opportunities. b. economic problems in central america and u. s. job demands collide to create a surge in illegal immigration. c. collapsing central american economies drive many workers out of their nations; simultaneous u. s. job demands lure immigrants. d. surges in illegal immigration are caused by the combination of economic pressures at home and opportunities abroad.