The US president, Donald Trump, has made public the tariffs he intends to slap on imports from another group of countries, including Brazil, from the start of August. The chipmaker Nvidia has become the first company in the world to reach a market value of $4tn on Wednesday. David Harper hears from experts. And Donald Trump has said the United States is shifting from aid to trade in its relationship with Africa as he welcomed five presidents from the continent to the White House.