单选题 PM2.5 particles are thought particularly damaging to health because they can ______ deep into the lungs.
  • A. dive
  • B. penetrate
  • C. elevate
  • D. dig
【正确答案】 B
【答案解析】dive：潜水，跳入水中；penetrate：进入，艰难地进入；elevate：升高；dig：挖，挖掘。