“不是第一选择”可以用英文表达为“not the first choice”或“not the top choice”。这个短语的来源可能源于人们在做决定或选择时，往往会有一个清单或者层次，其中第一选择是最优先考虑的选项。因此，“不是第一选择”就表示这个选项并不是最优先考虑的选项，而是次要的或者替代的选择。

下面是一些例句：

I wanted to go to the beach for my vacation, but the cost of fpghts and hotels was too high, so I ended up going to the mountains instead. The mountains were not my first choice, but they were still a great option. (我本来想去海边度假，但是飞机和酒店的费用太高了，所以我最终去了山上。山上不是我的第一选择，但仍然是一个很好的选择。)

I appped to several universities, but I got rejected from all of my top choices. The university that accepted me was not my first choice, but it's still a good school and I'm happy to go there. (我申请了几所大学，但我的所有首选大学都被拒了。接受我的大学不是我的第一选择，但它仍然是一所好学校，我很高兴去那里。)

I wanted to buy a car, but the one I really wanted was too expensive. I ended up buying a cheaper model that was not my first choice, but it still meets my needs and I'm happy with it. (我想买一辆车，但我真正想要的太贵了。我最终买了一个更便宜的模型，它不是我的第一选择，但它仍然满足我的需求，我很满意。)