Warplanes fly over Dallas, Texas, the United States, on May 22, 2020. Some historic warplanes flew over Dallas to honor frontline workers of the COVID-19 pandemic on Friday. (Photos: Xinhua)

Warplanes fly over Dallas, Texas, the United States, on May 22, 2020. Some historic warplanes flew over Dallas to honor frontline workers of the COVID-19 pandemic on Friday.

Warplanes fly over a hospital in Dallas, Texas, the United States, on May 22, 2020. Some historic warplanes flew over Dallas to honor frontline workers of the COVID-19 pandemic on Friday.

Warplanes fly over Dallas, Texas, the United States, on May 22, 2020. Some historic warplanes flew over Dallas to honor frontline workers of the COVID-19 pandemic on Friday.