Bikers perform motor acrobatics during the 14th Motor Festival, organized at the OAKA stadium from May 3 to 5 in Athens, Greece on May 4, 2019. (Photo: Xinhua)

A racing car performs during the 14th Motor Festival, organized at the OAKA stadium from May 3 to 5 in Athens, Greece on May 4, 2019. (Photo: Xinhua)

Photo taken on May 4, 2019 shows the engine of a racing car during the 14th Motor Festival, organized at the OAKA stadium from May 3 to 5 in Athens, Greece. (Photo: Xinhua)

A racing car performs during the 14th Motor Festival, organized at the OAKA stadium from May 3 to 5 in Athens, Greece on May 4, 2019. (Photo: Xinhua)

Two bikers perform motor acrobatics during the 14th Motor Festival, organized at the OAKA stadium from May 3 to 5 in Athens, Greece on May 4, 2019. (Photo: Xinhua)

A biker performs motor acrobatics during the 14th Motor Festival, organized at the OAKA stadium from May 3 to 5 in Athens, Greece on May 4, 2019. (Photo: Xinhua)