As Russia signs a deal to provide more oil and gas to China, how close are economic ties between both countries?

<p>From the BBC World Service: It&#8217;s a pretty big deal too – China is the world&#8217;s biggest energy consumer. But Beijing is being cautious about how much it supports Moscow, especially when it comes to the build-up of Russian troops at Russia&#8217;s border with Ukraine. And, scientists in South Africa say they&#8217;ve produced a version of Moderna&#8217;s COVID-19 vaccine.</p>