Existing Telescopes Are Capable of Detecting Radio Signals Similar to Those

Multiple Choice

Existing telescopes are capable of detecting radio signals similar to those generated by humans from

A) about a dozen or so of the closest stars.
B) any star around which planets have been detected.
C) any star within a 100 pc or so of the solar system.
D) stars in giant elliptical galaxies since these stars, being oldest, are most likely to have advanced civilizations.