他大胆的声明是对总统权威的挑战。

His bold statement was a ___challenge to the authority of the President.

杰克显得孩子气的唯一一次是当他挑战拉尔夫领导权的尝试失败后，他羞愧地哭了。

The one occasion in which Jack seems childish is when his ___challenge to Ralph's leadership fails and he weeps with humiliation.

她的诉讼对公司的政策构成了重大挑战。

Her lawsuit posed a significant ___challenge to the company's policies.