They could still invalidate Fourth Amendment protections when facing severe， urgent circumstances， and they could take reasonable measures to ensure that phone data are not erased or altered while a warrant is pending.
1.重点词汇及短语：
invalidate v. 使无效；证明(信念或解释)是无效的
severe v. 非常严重的；困难的
take reasonable measures to 采取合理的措施去……
warrant n. 令状，许可
pending n. 在等待……之际
2.句子成分分析：本句是一个由and连接的并列句。and前面的主干结构为They could still invalidate Fourth Amendment protections...。when facing severe， urgent circumstances是时间状语从句，由于face的逻辑主语与主句主语一致，因此省略主语和系动词，face用现在分词形式。and之后的句子主干结构为they could take reasonable measures...。to ensure that...pending是目的状语，that引导的从句作ensure的宾语。状语从句中的省略原则是：如果从句主语与主句主语一致，或从句的主语是it，可省略从句的连接词、主语和be动词，只保留分词和其它成分，从而使语言更加简洁明了。比如时间状语中的省略、地点状语中的省略、让步状语从句中的省略等。例如：The river is clean where (it is) deep.
