People sing songs during a wreath-laying ceremony in front of Martin Luther King Jr. Memorial in Washington D.C., the United States, Jan. 15, 2018. Various activities are held on the third Monday of January each year throughout the United States to honor the civil rights leader Martin Luther King Jr., who was born on Jan. 15, 1929 and was assassinated in 1968. (Xinhua/Yin Bogu)