"A plethora (singular) of questions <b>was</b> asked" sounds incorrect to me.<br/><br/>In this case, I'd lean toward the object of the preposition, <i>questions, </i>and make it a plural verb, <i>were.</i><br/><br/>But:<br/><br/>"Plethoras of questions WERE asked" sounds more viable and natural to me.<br/><br/>Or:<br/><br/>"A plethora of controversy surrounds (NOT: surround) the issue."<br/><br/>Do you agree?<br/><br/>Thanks.