Respuesta :
B. Memorized in his head
That way no one can get his password! A sticky note can be misplaced and someone can see it physically, his best friend might forget it and also go into Paul's account which is not safe, written down and kept at home is safe but what if Paul forgot his password? It is best for Paul to memorize his school password!
The correct answer is D. written down and kept at home.
Writing a sticky note in his desk could be unsafe because anyone could read it; memorizing it in his head could only be an option if he had a very good memory; telling it as a secret to his best friend could be unsafe too, it is always better not to reveal this kind of things.
The best option is writing it down and keep it at home where no one can see it.