Which instrument is used to dilate an opening or passage in the body for examination?

The appropriate instrument for dilating an opening or passage in the body for examination is a speculum. This tool is specifically designed to widen or open bodily cavities such as the vagina or rectum, allowing healthcare providers to gain better visibility for examination or procedures.

In contrast, a sphygmomanometer is used to measure blood pressure, while an endoscope serves not only for visualization inside the body but also to perform minor surgeries; it does not primarily function as a dilator. A tonometer measures intraocular pressure in the eye and is not involved in dilating passages. Thus, the speculum is the most accurate choice for the purpose of dilation to facilitate examination.