It was not until the 1860s ______ Abraham Lincoln declared the last Thursday of November to be a national holiday.
    A. whenever                                  B. that
    C. when                                        D as
 
【正确答案】 B
【答案解析】 本句为强调句，用“It+be动词+被强调部分+that引导的从句”来突出重要的信息，属信息焦点前移。所以答案为B。