What's the matter______ they still haven't answered the telegram?填了that,

What's the matter______ they still haven't answered the telegram?填了that,
What's the matter______ they still haven't answered the telegram?填了that,

What's the matter______ they still haven't answered the telegram?填了that,
that 引导的同位语从句,问他们还没回电报这事怎么了