Can you spot what's wrong with these 2 sentences?

Original: Determine if its necessary to modify the usual treatment regime for a patient in order to enable them to better tolerate the associated stress.

My corrections: Determine if it’s necessary to modify the usual treatment regime for a patient in order to enable him or her to tolerate the associated stress better.

Original: Because they were run over by a car, the police could not return Mary’s glasses.

I'm not sure about this one...but I think it could maybe be: "Because they had been run over by a car, the police could not return Mary's glasses.

My corrections.
Determine if it's necessary to modify the usual treatment regime for a patient in order to enable them to better tolerate the associated stress.

The second sentence seems good on its own.

Problem with Sentence 1:
Mixture of singular ("a patient") and plural ("them").

Problem with Sentence 2:
Sentence is ambiguous. WHAT was the "they" that was run over a car -- the police or the glasses?

Fixing these sentences for your homework will have to be done by you.

Problem with Sentence 1:
Mixture of singular ("a patient") and plural ("them").

"them" as a singular pronoun is fine. there have been some arguments over whether it's better to use a singular "they," generic "he," or the more newfangled "he or she" in reference to a person of unknown gender. but the problem has never really been settled to everyone's satisfaction. all 3 of those choices remain equally legitimate, depending on style and preference.

Problem with Sentence 1:
Mixture of singular ("a patient") and plural ("them").

"them" as a singular pronoun is fine. there have been some arguments over whether it's better to use a singular "they," generic "he," or the more newfangled "he or she" in reference to a person of unknown gender. but the problem has never really been settled to everyone's satisfaction. all 3 of those choices remain equally legitimate, depending on style and preference.

I studied English back in college.

I didn't get a degree to help someone on /prog/ with their homework, but I guess I could provide some assistance.

My corrections: Determine if it’s necessary to modify the usual treatment regime for a patient in order to enable him or her to tolerate the associated stress better.

This sentence can be shortened, reorganized, and cleaned up. Remember that less is more when it comes to proper English.

Original: Because they were run over by a car, the police could not return Mary’s glasses.

You need to make it clear what "they" is referring to (the police or the glasses).

I think you mean treatment regimen and not regime.

"Because they were run over by a car, the police could not return Mary’s glasses."

I'd go with this:

"Because they were run over by a car, the police could not return him or her glasses."

First sentence has an extraneous line and flows better as:
Determine if it's necessary to modify the usual treatment regime for a patient to better tolerate the associated stress.

For the second one, no sentence should begin with "because" and should read:
The police could not return Mary’s glasses because they were run over by a car.

I think a sentence can begin with "because" if needed, but in this instance there is no indication for such need.

I would write it:

The police could not return Mary’s glasses because the glasses had been run over by a car.

I would actually like to hear if anyone has an objection to this because English is not my first language.

"Regime" should be "regimen."

http://dictionary.reference.com/browse/regimen