单选题 Of the thousands of varieties of bird species in North America,______bright red plumage, like the cardinal, are most often designated as state bird.
【正确答案】 A
【答案解析】解析：此空要求填句子的主语且要做定语从句的先行词，同时还要有定语从句的主语和谓语，A符合题意。