英语中表达选择考研的说法有多种，以下是一些常见的表达方式：
I have decided to take the postgraduate entrance exams.
I have to choose to take part in the postgraduate entrance exams.
I have chosen to prepare for the postgraduate exam.
I am going to take part in the entrance exams for postgraduate schools.
这些句子都明确表达了选择参加研究生入学考试的决定和意愿。根据具体的语境和需要，可以选择其中任意一种表达方式。例如：
如果你已经做出了决定，可以说：“I have decided to take the postgraduate entrance exams.”
如果你是在描述一个必要的选择，可以说：“I have to choose to take part in the postgraduate entrance exams.”
如果你是在表达你的计划或准备，可以说：“I have chosen to prepare for the postgraduate exam.”
如果你是在描述未来的计划，可以说：“I am going to take part in the entrance exams for postgraduate schools.”
希望这些表达对你有所帮助。