Past Tenses, Present Tenses and Future Tenses

The 1st principal form without ‘to’ e.g. Nurses look after patients in hospitals.

In questions and negatives we add ‘do’. Do nurses look after patients in hospitals?
Yes, they do./No, they don’t.
Nurses don’t look after patients.

In the 3rd pers. in Sg. we add ‘-s’,’-es’. A nurse looks after patients in a hospital.

In questions and negatives we add ‘does’ Does a nurse look after patients?
Yes, she does./No, she doesn’t.
A nurse doesn’t look after patients.

But: She is thirteen
Is she thirteen?
Yes, she is./No, she isn’t.
She isn’t thirteen.…