❶Before the early 1800s, most Americans did not know how to tell time. ❷Most, in fact, did not even own clocks. ❸The seasons and the rising and setting of the sun were their time guideline. ❹But Americans' relationship with time changed greatly in the mid-1800s as many New Englanders shifted from farming to factory work. ❺Hundreds of thousands of factory workers had to adjust to a new sense of time. ❻Bells signaled the beginning and end of work shifts and mealtimes. ❼The first dawn bell might begin their days at 4:30 a.m. ❽They were expected to go to bed when a curfew bell sounded. 本段主题思想是哪句?_______