面对证据，他完全哑口无言。

When confronted with the evidence, he was completely ___at ___a ___loss ___for ___words.

如果要安慰如此悲伤的人，我会不知该说什么。

I'd be ___at ___a ___loss ___for ___words if I had to console someone in such grief.

魔术师的最后一个戏法让全场观众都张口结舌。

The magician's final trick left the entire audience ___at ___a ___loss ___for ___words.