那个句子缺了一个冒号。

There's a ___colon missing in that sentence.

使用冒号来引入一个列表：苹果、香蕉和橙子。

Use a ___colon to introduce a list: apples, bananas, and oranges.

老师解释说冒号用于例子之前。

The teacher explained that a ___colon is used before an example.