单项选择题 Although he was ------- in his efforts to persuade us of the justness of his cause, his past history, ...... with failures, prevented us from being any more than skeptical at his words.（）

单项选择题 While the causes of the Cretaceous-Tertiary extinction have received the most attention, Alvarez's paper points out work on the other major mass extinctions that may also be ------- for the tragedy.（）

单项选择题 Sadly, Americans of every ethnicity still demand ideological ------- among their own kind--although we're all multiculturalists now, we're much more ...... discussing diversity across the rainbow than within each color.（）