Let's take a look. This is a strengthen with a sufficient premise question. We're looking for a premise that, if true, would make the argument valid.
The conclusion in the stimulus is attempting to explain why there is a greater abundance of craters in geologically stable regions. It says it's because these regions have lower rates of destructive geophysical processes. In order to make the argument valid, it would be great if we could eliminate alternative explanations for the phenomenon. There are possible alternative reasons for these craters being in these reasons. It could be pure coincidence. However, if we knew for certain that these craters weren't in these regions by coincidence (or some other type of explanation), then this would make the argument in the stimulus valid.
(D) says, "Actual meteorite impacts have been scattered fairly evenly over the Earth's surface in the course of Earth's geological history."
If (D) is true, then it guarantees the conclusion, as it rules out an alternative explanation (that the areas with a greater concentration of impact craters have just been hit with more meteorites). This eliminates coincidence as an alternative explanation, making the argument valid.
Does this make sense? Let us know if you have any other questions!
