When two pyrimidine [py-RIM-i-deen] bases are adjacent on a DNA strand, exposure to UV light will commonly lead to formation of a cyclobutane ring between them, resulting in a bulky lesion in the DNA. The normal replicative polymerases [pol-uh-muh-RAYS-uhs] cannot use this as a template, and the lesion often results in mutation if it cannot be repaired. Which of the following is an example of this lesion formed by UV exposure of neighboring pyrimidines [py-RIM-i-deens]?