Final answer:
The concerted search for life outside Earth is focused on Mars due to its past habitable conditions and potential for water, alongside investigations into Europa's sub-ice ocean and the study of habitable exoplanets.
Step-by-step explanation:
Scientists have begun a concerted search for life outside of Earth primarily on Mars (C).
Exploration for extraterrestrial life is a focal point of modern space science. Mars, with its similarity to early Earth conditions and potential for ancient and contemporary liquid water, is a primary candidate for these searches. Spacecraft have been sent to probe its surface and analyze samples to find evidence of life. Europa, one of Jupiter's moons, is another key interest, where an ocean beneath its icy surface could harbor life.
The study of exoplanets, planets orbiting other stars, is also significant, as some may have Earth-like conditions that could support life. The Search for Extraterrestrial Intelligence (SETI) investigates whether intelligent life exists elsewhere in the universe. Collectively, these efforts aim to address the profound question of whether life on Earth is unique.