Christian Mango, a 10-year-old from Greensboro, worried about the lives of 6.5 million people being threatened by pollution. He worried about what would happen to the glaciers. And he worried about the worsening weather. So he wrote to U.S. Rep. Virginia Foxx, a Republican from Banner Elk, N.C., with a solution: a $5,000 tax rebate from the federal government for new electric vehicles. The letter, obtained by McClatchy through Foxx’s office, was submitted through Christian’s fourth-grade teacher. “Please enjoy this student’s hard work and passion,” the teacher wrote. Foxx responded to the student with a strongly worded letter that has gained national attention — and criticism — after Christian’s mother, Emily Mango, posted the congresswoman’s letter to her son on Instagram .…