The border crossing between San Ysidro (California) and Tijuana (Mexico), considered the busiest in the world, closed temporarily for a security exercise conducted by the Office of Customs and Border Protection (CBP).It is the second time in the last two months that said port of entry has suspended its operations because of these exercises.The first exercise carried out last November was made after some Central Americans who came to Tijuana in the migrant caravan tried to cross the border fence, however, today's took human rights activists...