Self-study
The axis of Earth's daily rotation is tilted with respect to the plane of its orbit at an angle of roughly 23 degrees. ████ █████ ███ ██ ████ ██████ ██████ ████ ██ ███ █████████████ █████████ ██ ███████ ██████ ██████ █████ ███████ ████ █ ██████ ███ ████████ ████ █████ █ ████████ ███████ ██ ███ ███████ ███ ████████ ██ ███████ █████ █████ ███ ████████ ███ ████ ████ █████ ██████ █████ ██ ██████ ███████████ ███████ ███ ██████ ███████ █████
Summary
The Earth’s large moon is necessary to keep the Earth’s axis tilt angle stable. This stability is necessary for the Earth to support life. Mars lacks a large moon and does not have a stable axis tilt angle. Mars cannot support life.
The stimulus can be diagrammed as follows:
Notable Valid Inferences
Without the Earth’s moon, the Earth would not be able to support life. Mars lacks a necessary condition for life—a stable axis tilt angle. This ensures Mars cannot support life.
14.
If the statements above are █████ █████ ███ ██ ███ █████████ ████ ████ ██ ████ ██ ███ █████ ██ █████
a
If Mars had █ ████████████ █████ ██████ █████ ████ █████ ██ ████ ██ ███████ █████
This could be false. A large moon may stabilize Mars’s axis tilt angle, fulfilling a necessary condition for life on Mars. However, this does not mean Mars fulfills any other conditions for supporting life. A stable axis tilt angle is necessary for life—not sufficient.
b
If Earth's Moon ████ ██ █████ ███████ ██████ ███████ ███████ █████ ██ ██████ ██ ███████ █████
This must be true. As shown below, when we take the contrapositive of the conditional claims in the stimulus, we see that the absence of the Moon would mean the Earth would be unable to support life. In other words, the Moon is necessary for Earth’s ability to support life.
c
Any planet with █ ███████ ████████ ████ ████ ███ ███████ █████
This could be false. A stable axis tilt angle is a necessary condition for a planet’s ability to support life—not a sufficient one.
d
Gravitational influences other ████ █████ ████ ██████ ██ ██ ██████ ██ ███ █████████ ██ ███ ████ █████ ██ ██████ ███████ ██ ██████ █████
This could be false. While the stimulus focuses on moons and their impact on the planets’ axis tilt angles, it does not suggest that moons are the only important factor affecting the planets’ axis tilt angles.
e
No planet that ███ ████ ████ ███ ████ ███ ███████ █████
This could be false. We know Mars has very small moons and cannot support life. Given the information in the stimulus, however, it could be true that a planet has multiple moons with at least one large enough to keep the planet’s axis tilt angle stable.