The correct answer is A. Colonoscopy.

The image is a sebaceous adenoma, and the question describes keratoacanthomas on the anterior shin, thus this patient should undergo colonoscopy to evaluate for colon cancer. Given this constellation of symptoms one must evaluate for Muir-Torre syndrome.

The remaining choices are incorrect.

References: Iacobelli J1, Harvey NT1, Wood BA2. Sebaceous lesions of the skin. Pathology. 2017 Dec;49(7):688-697. doi: 10.1016/j.pathol.2017.08.012. Epub 2017 Oct 25.