Which of the following statements is true? Over the last fifty years, the risk spread between Aaa bonds and Baa bonds always remained positive except in 1998. The risk spread between Aaa bonds and Baa bonds became negative only in the mid-1960s. For most of the last twenty years, the risk bread between Aaa bonds and Baa bonds remained negative. Over the last fifty years, the risk spread between Aaa bonds and Baa bonds never became negative