Answer:
The most correct way to write this would be U.S.,
Explanation:
I have a few opitions which are all techincally grammaticlly correct.
First, the radio signals came from the United States; then they came from Canada. (More formal)
...came from the U.S. but then.... (also grammatrically correct)
...from the U.S., then from ....
hope this helps :)
Checked out
Checked out is not domain specific language. When talking about medical visits, checked out is an informal term for having a medical evaluation. A check-up is a routine procedure done yearly that is normally called a physical in the medical field. A fall is a fall. There is no other domain specific vocabulary that can change this. Clinic and injuries are all typical domain specific terms that can be applied in medical situations.
The answer is A, it contains a fragment
Hope this helps!