A common HDTV format is?

The correct choice is 720p, which is indeed a common HDTV format. The "720" refers to the vertical resolution of the image, which consists of 720 lines, while the "p" stands for progressive scan. In progressive scanning, each frame of video is drawn line by line in sequence, which results in smoother motion and a clearer picture, especially for moving images. This format is widely supported across various broadcasting and streaming services, making it a popular choice for high-definition television.

In the context of the other choices, while 480p is considered standard definition (SD) and 4K represents ultra high-definition (UHD), 1080p is also a high-definition format but is less common than 720p in certain broadcasting contexts due to the increased bandwidth required for transmission.