— Did Jack _____ having taken some books without telling anybody?

— Yes, he did. He said he took three books. [ ]

A. imagine

B. allow

C. attempt

D. admit

资料中谈到PM2.5治理需要漫长的过程，关于治理PM2.5的问题，政府应采取什么样的解决措施
要求：分析条理清楚，措施得当，字数不超过300字。