【题目】It is through years of research ________ scientists have discovered the relationship between social media addiction and depression.
A. that B. before
C. since D. when
在线课程【答案】A
【解析】
考查强调句型。句意：正是通过多年的研究，科学家们发现了社交媒体成瘾和抑郁症之间的关系。此处是强调句型：It is +强调部分+that+---。故选A。