Why was slave labor not as important to the north as it was to the south?

This question is based on the following passage. except for a few pigeons, central park was deserted. mist hung above the chilled grass. patches of old snow, scattered here and there, looked like white puddles. the sun hung just above the horizon, casting red and orange streaks across low-hanging clouds. the portly, gray-haired gentleman jogging down the path looked out of place. for one thing, he was dressed in ordinary street clothes, not a sweat suit. also, every few seconds, he looked anxiously back over his shoulder. coming closer to me, i saw that his face was flushed. he was panting, almost gasping. abruptly, looking this way and that, he moved behind a tree. seeming not to notice my presence, he stood with his back against the trunk, panting heavily. after a moment, he poked his head out to survey the path. it was still empty, except for a squirrel that dashed across the path like a furry dart. i checked my watch. it was now 7: 30. mentally marking the time, i aimed my camera toward the man's face. 20. from the paragraph, you can conclude that the portly man is afraid of something. which one of the following elements gives the strongest evidence for that conclusion? a. he isn't dressed in a jogging suit. b. he's panting. c. he hides behind a tree. d. he's running in a nearly deserted park.