To edit the provided sentence correctly, we need to add punctuation marks to separate titles, names, and the time. Here's the original sentence with the necessary punctuation added:
"Professor Gray, Mr. Michaels, Dr. Gunn, and Ms. Foster usually arrived at the office by 8:30 a.m."
Now, counting the punctuation marks:
- Comma after "Gray"
- Period after "Mr"
- Comma after "Michaels"
- Period after "Dr"
- Comma after "Gunn"
- Period after "Ms"
- Colon in "8:30"
Total: 7 punctuation marks.
So the correct answer is 7.