Given the attitude of the grandfather portrayed in the problem, the most likely answer is
B) Go to the doctor regularly because he can monitor his health before problems get severe.
This would be because you are reminded, "prevention is the best medicine", and the answer B provides the precaution that is recommended.
It is important to write application correctly cuz if the patient gets the wrong medical advice or takes the wrong pill based on your handwriting it will cause error
They can if they want to, but if they do they will infect whoever they are doing it with. No one can stop them. But if you are looking for a definitive answer then no, it is not okay at all because of the risk they are putting other people at. Especially because STDs are with you forever, they never go away.
Hope this helps!!