Identifying candidate keys and primary keys

Hello guys, this one is for one of my assignments. I want explanations
and hints only.

I'm still confused with the concepts of candidate keys and primary
key. We have a patient medication form from an hospital with these:

Heading: Patient number, Full name, Bed number, Ward number, Ward
name.
Then a table with this columns: drug number, name, description,
dosage, method of admin, units per day, start date, finish date.

I have to find all the candidate keys and primary keys. I think
candidate keys are the minimal superkeys.

I have found {Patient number, Ward number, Ward name}. I have excluded
{Patient number, Ward number, Ward name, Full name} and {Patient
number, Ward number, Ward name, Full name, Bed number} which are also
superkeys but contain more attributes.

This means that I have found only one candidate key, and this is also
the primary key I have found (a composite).

Since the question was "identify all the candidate keys" I thought
maybe I dont really understand the concepts...

thanks for any help.
.

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