4 D, d

D, d
n (pl D´s, d´s )
1 the fourth letter of the English alphabet 英语字母表的第四个字母
    `David´ begins and ends with a `D´/D. David一字的开头和结尾都是D.
2 D (music 音) the second note in the scale of C major C大调音阶中的第二音或音符.
3 D academic mark indicating a low standard of work 学业成绩为低等的评价符号.