What strategies and electromagnetic frequencies are thought to be the most logical for long-range communication across the universe with other intelligent beings?
A. explosion of nuclear devices at specific intervals and in specific patterns across Earth when we are closest to a nearby star
B. night-by-night photography of nearby stars at hydrogen Balmer wavelengths
C. continuous radio and microwave listening and transmitting at frequencies at which the natural radio sky noise background is low
D. X-ray surveys of space at appropriate times (e.g., when Earth is closest to nearby stars in its orbit), in view of the penetrability of space at these wavelengths