There are fewer boys than girls in my class. 我班上男生比女生少。

在比较结构中，than 一般用作连词。例如：

1. Thomas arrived earlier than the others. 托马斯比其他人早到。

2. She speaks more English than she did last term. 她讲英语比上学期要多。

3. It's colder in Beijing than in London in winter. 在冬天，北京要比伦敦冷。

4. The students in Class 2 are more active than those in Class 1. 二班的学生要比一班活跃。

在There are fewer boys than girls in my class. 这个句子中，than 同样看作连词，后面跟了省略了there are 的句子：There are fewer boys than (there are) girls in my class.

有时候，than 后面的成分似乎不完整，其实，是连词than 后面的部分省略了有关成分。例如：

1. Thomas arrived earlier than the others. 托马斯比其他人早到。

=Thomas arrived earlier than the others did.

2. It's colder in Beijing than in London in winter. 在冬天，北京要比伦敦冷。

=It's colder in Beijing than it is in London in winter.

3. The students in Class 2 are more active than those in Class 1. 二班的学生要比一班活跃。

=The students in Class 2 are more active than those in Class 1 are.

4. That was infinitely better than his last film. 这比他上一部电影不知胜过多少倍。

=That was infinitely better than his last film was.

5. Mary would rather travel by train than by plane.  玛丽宁可乘火车而不愿乘飞机旅行。

=Mary would rather travel by train than she does by plane. 

6. I like her more than he.我比他更喜欢她。

=I like her more than he does.

7. I like her more than him.我喜欢她胜过喜欢他。

=I like her more than I do him.