Posters are seen through the gate of the National Zoo in Washington D.C., the United States, July 23, 2020. The number of COVID-19 cases in the United States surpassed the 4 million mark Thursday to reach 4,005,414 as of 3:04 p.m. local time (1904 GMT), according to the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University. (Xinhua/Liu Jie)