Final answer:
Active SETI differs from traditional SETI in that it involves sending signals into space, rather than solely listening for them. This proactive approach is meant to announce our presence to any extraterrestrial intelligence that might be listening.
Step-by-step explanation:
The question asks about the difference between traditional SETI efforts and what is known as active SETI. Traditional SETI, or the Search for Extraterrestrial Intelligence, primarily involves the use of radio telescopes to listen for signals that may come from other civilizations. This is often termed as passive SETI. In contrast, active SETI or Messaging to Extra-Terrestrial Intelligence (METI) goes a step further by sending signals into space, in attempts to announce our presence and potentially start a form of interstellar communication.
Our current efforts for SETI are focused on detecting various types of signals, such as radio waves or leakage signals that could indicate the existence of advanced civilizations. Radio telescopes like the Arecibo dish, Allen Telescope Array, and Green Bank Telescope are some of the major instruments that have been used for this purpose. While efforts to listen continue, the debate on whether to engage in active SETI involves considerations of humanity's readiness to make contact and who would represent Earth in such a communication.
Therefore, the answer to the student's multiple-choice question would be: b) Active SETI involves sending signals to space.