There’s no telling the dog might cause her to drive into a crowd of pedestrians括号里只能是填that或when应该选什么为什么

应该选"what"，因为句子中缺少一个合适的词来引导主句和从句之间的关系，而"what"可以引导一个名词性从句，在句子中起到连接作用。句子的正确表达应该是：There’s no telling what the dog might cause her to drive into a crowd of pedestrians.