-Anitha Dunga : Subject Matter Expert at Edumarz
Answer : In condition (c) the person is most likely to fall sick.
In condition (c) when your friend is suffering from measles infection which is contagious. When you are in contact with your friend there is a possibility of getting infected with the infection of measles. Measles is an airborne respiratory disease that can be spread to the other person from the infected person when he/she is coughing or sneezing. So when you are close to the person who has the infection it causes you to get infected from the disease.
Also this measles can be transmitted from one person to the other by touching the contaminated surface like blankets, handkerchief and other used by the infected person and als it can be transmitted by touching the contaminated surface with the droplets from coughing and sneezing of the infected person.
In condition (a) there is no chance of getting infection from any disease because while writing your exam you will not come in contact with anyone.
In condition (b) chances of falling sick were less, when you are traveling in bus or train probably you will not get close to anyone so, they are less chances of getting infection and becoming sick.