【正确答案】 D

【答案解析】此题属于语法题。本句中Concerns were raised是主句部分，witness might be encouraged...是从句，修饰名词concerns；而从句中主谓齐全，应该是concerns的同位语，故只有选项[D]that可引导同位语从句，是正确答案。选项[B]when在语意上与本句不符。选项[A] what不可引导同位语从句，一般引导主语从句或宾语从句，例如：What you have said confused me．又如：I will tell you what have happened．选项[C]which可用于引导主语从句、宾语从句或定语从句，考生应特别注意which引导的定语从句和that引导的同位语从句，要记住前者在从句中充当主语或宾语，而后者在从句中不充当成分，试比较：
1)The news which excited us is that our team has won．
2)The news that our team has won excited us all．