Question #N429

The following text is from a science textbook about the anatomy of the human eye. The human eye is an organ that is responsible for sight. The retina is a light-sensitive layer of tissue that is located at the back of the eye and contains specialized cells called photoreceptors that are responsible for converting light into electrical signals that the brain can interpret. Which choice completes the text so that it conforms to the conventions of Standard English?

The retina, which ____ at the back of the eye, contains specialized cells called photoreceptors.
A. is located
B. locates
C. is locating
D. locate