The correct option is A radio waves
The Giant Meterwave Radio Telescope (GMRT) detects radio waves having wavelengths of about a metre coming from heavenly bodies to study those bodies.
It has a collection of 30 dishes, each having a diameter of 45 m spread over an area of 25 km across. Radio waves incident on each of the dish is reflected to a radio receiver. This information is then gathered and compiled by computers.