单选题 The invisible rays of the ______ beyond the violet end are called the ultraviolet rays.
A. speculation B. spectrum C. sleet D. range

【正确答案】 B
【答案解析】[解析] B项spectrum“光谱”符合题意。其他三项都与题意不符：speculation猜测，投机；sleet冰雨；range范围。