一门

luó ji xué shì dān dú yī mén kè

逻辑学是单独一门课。

Logic is a separate subject.

shù xué shì yī mén chōu xiàng xué kē

数学是一门抽象学科。

Mathematics is an abstract discipline.

shàng yī mén jì suàn jī kè chéng duì nǐ yǒu lì

上一门计算机课程对你有利。

It will be to your advantage to take a computer course.