Answer:
Hmm. You've made an error here.
Follow me as I explain....
A complex sentence is made up of an independent clause and a dependent (subordinate) clause. (The order of the clauses doesn't matter.)
Your instructions say to add a subordinate clause to the clause you have provided, but as I have just explained, the other clause MUST be an independent clause -- yet what you have provided is NOT an independent clause.
I believe what you meant to write was: "The police officer was very concerned."
Once we correct that error, then I can now provide you with a couple possible answer examples.
dependent (subordinate) clause
The police officer was very concerned because the suspect would not stop fidgeting in his chair.
dependent (subordinate) clause
When he learned that the suspect lived just a few houses away from him, the police officer was very concerned.
Explanation:
