听力原文： (25) The world's largest drug company is embroiled in a global controversy over whether it tested an unapproved drug on sick children in Nigeria without their full understanding. The case involving Pfizer raises questions about how to protect human subjects as American companies conduct more and more drug trials around the world. VOA's Leta Hong Fincher has this report. In 1996, a meningitis epidemic hit the Nigerian state of Kano. Researchers from the American company, Pfizer, treated 100 Nigerian children with the experimental drug, Trovan. The Nigerian government and the Kano state government are suing Pfizer over the drug trial. (26) They say it caused the deaths of 11 children and seriously disabled others. Why is the world's largest drug company embroiled in a global controversy?