1. 英语字母表的第3个字母
    C is the third letter of the English alphabet.

2. C大调音阶中的第一音;C音
    In music, C is the first note in the scale of C major.

3. （作业、考试等）丙等，第三等，C级
    If you get a C as a mark for a piece of work or in an exam, your work is average.

4. (用于日期或数字前)约,大约
    c. is written in front of a date or number to indicate that it is approximate. c. is an abbreviation for (缩略 =) 'circa'.

    e.g. ...the museum's recreation of a New York dining-room (c. 1825-35).
           博物馆内对一家纽约餐厅(约1825-1835年)的再现

5. (用于首字母为C的一些单词的缩写,如 copyright, Celsius 等)
    C or c is used as an abbreviation for words beginning with c, such as 'copyright' or 'Celsius'.

    e.g. Heat the oven to 180?C.
           把炉子加热到摄氏180度。

6. see also: C-in-C;c/o