单选题 23.  It is during his spare time ______ Johnson has been studying a course in history.
【正确答案】 D
【答案解析】[考点] 强调句
分析句子结构可知,本句为强调句,其基本结构为“It is/was+被强调部分+that/who+其他”。本句强调的是时间状语during his spare time,所以应用that引导。故选D。
   约翰逊正是在业余时间一直学习历史课程的。