题目内容：

There are signs ___MP4 has become more popular with the young people Ain which Bthat C how D when
为什么选B

优质解答

__that_MP4 has become more popular with the young people 是一个同位语从句,修饰signs
,解释signs的具体内容.that引导同位语从句,that本身不作任何成分,但不能省略.