在'city'这个单词中，第三个字母是c。

In the word 'city', the third letter is ___c.

请弹奏C3这个音符。

Please play the note ___C3.

他这次考试得了C，算是勉强及格了。

He received a ___C on the exam, which means he barely passed.

在物理公式中，c通常代表光速。

In physics formulas, ___c often stands for the speed of light.

二氧化碳的分子式是CO2，其中包含一个C原子。

The formula for carbon dioxide is CO2, which includes one ___C atom.