Answer: C. Very Large Array
There are 28 radio antenna, which are essentially satellite dishes. Only 27 are in operation at any given time, leaving one to sit out for maintenance. Astronomers using this array were able to observe black holes, and also observe the formation of interplanetary disks, among many other applications as well.
The reason why so many dishes are used is to increase the faint signal that is received from such a long distance away (often lightyears away). The 27 dishes are effectively the same as having a single radio dish that is 36 km (22 miles) in diameter. Having such a impossibly massive satellite dish is not feasible, so it's more practical to go with 27 smaller dishes.