Here are my answers to OWL's *Commas after Introductions Exercise 1*, part B.
According to my understanding of the answer key [1], I got the last sentence wrong. Either I don't understand the answer key or I disagree with it. For details, see the very last sentence below and my comment on it.
https://owl.purdue.edu/owl_exercises/punctuation_exercises/commas/after_introductions_exercise_1.html :
> B. Add introductory commas where they are needed in the following sentences. [...]
>
> 1. To give Jane a good look at the university Mr. Benson drove up for the Day on Campus.
Add comma: To give Jane a good look at the university, Mr. Benson drove up for the Day on Campus.
> 2. Since the dog had started to run a way we had to scramble to catch him.
Add comma: Since the dog had started to run a way, we had to scramble to catch him.
> 3. Of course the movie that I had rushed to see didn't start on time.
Add comma: Of course, the movie that I had rushed to see didn't start on time.
> 4. Her secondhand car was in excellent condition when she bought it.
OK as-is.
> 5. As I mentioned the rules can be broken occasionally.
Add comma: As I mentioned, the rules can be broken occasionally.
> 6. Having decided to eat only natural foods he had to give up all of his favorite junk food snacks.
Add comma: Having decided to eat only natural foods, he had to give up all of his favorite junk food snacks.
> 7. To estimate the costs he consulted a repairman by phone.
Add comma: To estimate the costs, he consulted a repairman by phone.
> 8. To succeed in politics is not necessarily desirable.
OK as-is.
> 9. Making up his mind quickly Jared ordered lasagna while we were still reading the menu.
Add comma: Making up his mind quickly, Jared ordered lasagna while we were still reading the menu.
> 10. However he tried to use the bottle opener it wouldn't work.
If I understand the answer key for part B correctly, I got this one wrong. Supposedly, it's OK as-is.
I think "However he tried to use the bottle opener" is an introductory phrase that should have a comma after it: However he tried to use the bottle opener, it wouldn't work.
The introduction to part A says:
> If there is an error, put an X on the line and circle the error.
The introduction to part B doesn't mention Xs, but the answer key for part B [1] has three sentences labeled with an X: B.4, B.8, and B.10. It seems to me that these Xs indicate something other than an error, because no error is pointed out for those sentences.
I didn't add commas to B.4 and B.8, but I did add a comma to B.10.
[1]
https://owl.purdue.edu/owl_exercises/punctuation_exercises/commas/after_introductions_exercise_1_answers.html