Final answer:
The Moon does not crash into Earth because option d. it has a sufficient tangential speed, which, along with Earth's gravitational pull, keeps it in orbit as a result of centripetal force.
Step-by-step explanation:
The reason the Moon does not crash into Earth is due to its tangential speed. As the Moon moves, it has a tendency to continue traveling in a straight line due to inertia. However, the gravitational pull of the Earth provides the necessary centripetal force to keep it in orbit. If the Moon had no tangential speed, it would be pulled directly towards the Earth by gravity. Because it does move tangentially and at a speed that is sufficient to balance the gravitational pull, it continues to orbit instead of crashing.
As for the provided options, the correct answer would be (d) moon has a sufficient tangential speed. This is because when an object is in orbit, its centripetal acceleration towards the center of the gravitational force (in this case, Earth's gravity) is what keeps it moving in a circular (or more accurately, elliptical) path. The role of the Moon's mass and the gravitational pull of other planets is not directly relevant to why the Moon does not crash into the Earth in the context of this question.