Statement : The beaches are now full of people having a family holiday, having surfing lessons and engaging in other leisure activities such as para-sailing.
Which of the following can be the most immediate cause of the effect?

People are talking lessons and engaging in other activities
as well, hence (c) is the most complete cause. Other choices are not sufficient causes. For example, advertising may not be very effective and even if people come to beaches, they may not engage in many activities for which they may have to pay.