Questions 1–5.

Questions 6–10. Select the TWO correct answer choices.

Questions 11–15 are based on the passage below.

The 2015 direct detection of gravitational waves, ripples in spacetime predicted by general relativity a full century earlier, confirmed one of the last major untested predictions of Einstein's theory and opened what astronomers describe as an entirely new observational window onto the universe. Traditional astronomy relies on detecting electromagnetic radiation — visible light, radio waves, X-rays — emitted by cosmic objects, a method that fails entirely for events that produce little or no light, such as the merger of two black holes. Gravitational waves, produced whenever massive objects accelerate, propagate largely unimpeded by the intervening matter that can absorb or scatter light, meaning they carry comparatively undistorted information from events even when direct electromagnetic observation is impossible. The technical challenge in detecting these waves is immense: the instruments involved must measure distortions in spacetime smaller than one ten-thousandth the width of a proton, a sensitivity achieved only through multi-kilometer laser interferometers isolated from virtually every source of vibration on Earth. Since the initial 2015 detection, dozens of additional events have been recorded, including, in 2017, a black hole merger observed simultaneously in gravitational waves and, for the first time, in conventional telescopes as well — a landmark moment researchers call "multi-messenger astronomy," in which the same cosmic event is studied through fundamentally different physical channels simultaneously.

Questions 16–20 are based on the passage below.

The "Great Filter" hypothesis, proposed to explain the apparent absence of detectable extraterrestrial civilizations despite the vast number of potentially habitable planets in the observable universe, suggests that one or more improbable steps must occur between the formation of a planet and the emergence of a civilization capable of interstellar communication, and that this step (or steps) acts as a filter that few, if any, planetary histories successfully pass through. A crucial and unsettling question attached to this hypothesis is whether the filter lies behind humanity, already passed, or ahead of it, still to come. If the filter is behind us — if, for instance, the origin of life itself, or the emergence of complex multicellular organisms, is the truly improbable step — then humanity's continued survival and eventual expansion into the cosmos might be relatively likely, since we have already cleared the hardest hurdle. If the filter instead lies ahead, some undiscovered threshold that most civilizations fail to cross, perhaps self-destruction through advanced technology or resource exhaustion, then the silence of the cosmos offers little comfort: it would suggest that whatever obstacle destroys civilizations before they can spread across the stars likely awaits humanity as well. Proponents of the hypothesis stress that it cannot presently be resolved through observation, since we cannot yet distinguish which explanation accounts for the absence of detected civilizations, though some argue that recent difficulties predicting long-term technological or environmental stability lend weight to the more troubling possibility.