Student or Learner
"British authorities investigated the death and it was reported on 1 December that scientists at the Atomic Weapons Establishment had traced the source of the polonium to a nuclear power plant in Russia. On 3 December, reports stated that Britain has demanded the right to speak to at least five Russians implicated in Litvinenko's death, and Russian Foreign Minister Sergey Lavrov asserted that Moscow was willing to answer 'concrete questions.' "
How are "concrete questions" different from "specific questions"?
Please be aware that I'm neither a native English speaker nor a teacher.