What consists of groups of one, two, and three rectangular bars symmetrically arranged about the runway centerline?

The correct choice is indeed the Touchdown Zone Markings. These specific markings are crucial for pilots during landing, as they designate the portion of the runway where ideally, the aircraft should touch down. The markings consist of symmetrically arranged rectangular bars that are typically seen in groups of one, two, or three, running across the runway. Their placement and format help ensure that pilots have a visual reference to aid in making a safe and successful landing.

Other options, while related to runway design, serve different purposes. Runway Side Strips refer to the areas beyond the runway edges designed to enhance safety but do not provide landing guidance. Threshold Markings indicate the beginning of the runway usable for landing. Blast Pads serve as an area to accommodate jet blast and provide safety margins but do not assist with touchdown location or guidance. Each of these components is integral to runway operations, yet Touchdown Zone Markings are specifically tailored to assist with the landing phase by indicating optimal touchdown points on the runway.