"选专业"用英语可以说成"choose a major"或"select a major"。例如：

1. I need to choose a major for my undergraduate studies.

2. She is considering several majors before making a decision.

此外，如果你想要更具体地表达选择某个学科的专业，可以使用"major in"加上学科名称，例如：

1. I want to major in Computer Science.

2. She majored in Physics during her undergraduate years.

希望这些信息对你有所帮助。