Which does not contain a run-on sentence?
a. the big dipper is almost always visible in the northern hemisphere, so these stars make a good reference point.
b. the big dipper is almost always visible in the northern hemisphere these stars make a good reference point.
c. the big dipper makes a good reference point, these stars are almost always visible in the northern hemisphere.
d. the big dipper is almost always visible, these stars make a good reference point in the northern hemisphere.

A. It changes keys smoothly from one side of the sentence to the next. ", so" is a coordinating conjuction. It's sort of like the point that connects two train cars to each other. This also keeps it from being a run on sentence.

(Other conjuctions are: and, but, for, nor, or, and yet.)

the incorrect statement about jews is: d. jews began migrating to germany after the end of world war i. jews migrated throughout the world across many centuries, and that was also the case with germany, the migration began before the end of world war i, but there was an emigration wave before the start of the world war ii.

your answer is c) experiments with water vapor showed that elements combine in specific proportions.