Which of these combinations of words are commonly used, and which are not commonly used? Please correct

1. Her mother passed away due to skin cancer. (COMMONLY USED) - This sentence is commonly used and appropriate to express that someone"s mother has died because of skin cancer.
2. Does your country have a cost for prescriptions? (COMMONLY USED) - This sentence is commonly used and appropriate to ask if prescriptions have a cost in someone"s country.
3. In Britain, national security is funded through a separate tax, distinct from income tax. (COMMONLY USED) - This sentence is commonly used and appropriate to explain how national security is funded in Britain.
4. Healthcare is the largest expenditure in the nation"s budget. (COMMONLY USED) - This sentence is commonly used and appropriate to state that healthcare represents the biggest expenditure in a nation"s budget.
5. Are there private health insurance companies in your country? (COMMONLY USED) - This sentence is commonly used and appropriate to inquire about the presence of private health insurance companies in someone"s country.
6. Private dentists have high fees. (COMMONLY USED) - This sentence is commonly used and appropriate to state that private dentists charge high fees for their services.
7. She experiences a severe allergy and cannot be in a room with smoke. (COMMONLY USED) - This sentence is commonly used and appropriate to describe someone"s severe allergy, which prevents them from being in a room with smoke.

All of the provided combinations of words are commonly used and appropriate in their respective contexts. No corrections or changes are necessary.