1. Judy leads a charmed life she never seems to have a serious accident.

This sentence is correct

life, she

life; she

We have two independent clauses here and they must be connected somehow. We can't use the comma by itself without creating a comma splice.

2. The airport is about to shut down because of the snow and if the plane doesn't land soon it will have to go on to Boston.

This sentence is correct

snow, and

snow; and

snow. And We have two independent clauses connected with a little conjunction. Because of their complexity, it would be a very good idea to separate them with a comma.

3. The show begins at 7:30 make sure you're there before 7:15.

This sentence is correct

7:30, make

7:30. MakeOur second sentence is a directive based on what was said in the first sentence. Although the clauses are closely related, they still must be treated as independent clauses. We could connect them with a comma + so, or we can leave them as two separate sentences.

4. Marcellino always knew his way around the woods this is something he could always depend on.

This sentence is correct

woods; this

woods, thisThese clauses are clearly related; the pronoun 'this' connects the two clauses in meaning. However, they are both independent clauses and need to be connected with a comma + a little conjunction or they should be separated with a semicolon.

5. Having prepared himself well for the realtor exams and having exhausted everyone in the family with his requests that someone help him with the true-and-false drills, Jeffrey, who had never been a particularly good student in high school, knew he was ready to take on the greatest challenge of his life.

This sentence is correct

drills; Jeffrey

Jeffrey -- who had never been a particularly good student in high school -- knew

There is nothing wrong with that sentence as it is written. Remember that length has nothing to do with whether a sentence is a run-on or not.

6. Throughout history money and religion were closely linked there was little distinction between government and religion.

This sentence is correct

linked because there was

linked, there was In our revision we subordinated the second clause to the first with the subordinating conjunction 'because.' The comma by itself doesn't do the trick; it only creates a comma-splice.

7. The head of state and the religious leader were often the same person all power rested in one ruler.

This sentence is correct

person, all

person; all The semicolon can be used here to connect two nicely balanced and closely related ideas. The comma by itself creates a comma splice.

8. These powerful leaders decided what objects would serve as money their backing encouraged public faith in the money.

This sentence is correct

money. Their

money, their Although it would be possible to connect these two clauses with a semicolon, probably the best bet is to separate them and treat them as separate sentences. The comma by itself would create another comma splice; a comma + a little conjunction would probably not be an adequate solution to this run-on.

9. Coins were minted of precious metals the religious overtones of money were then strengthened.

This sentence is correct

metals, the

When coins were minted of precious metals, the . . . .

The comma by itself creates a comma splice. Instead of combining these independent clauses with a comma and a little conjunction, we have subordinated the first clause to the second with the subordinating word 'when'.

10. People already believed the precious metals to be divine so their use in money intensified its allure.

This sentence is correct

divine, so

divine; so

divine their

Although we have connected these two independent clauses with a little conjunction ('so'), we also need a comma to separate these clauses. We never use a semicolon and a little conjunction to connect independent clauses.