In the question below, three sentences are given

Solution

A talks about a concern expressed by students about whether they would be able to find a job matched to their skills and education; B introduces a different concern held by other students regarding the poor health of Spain. WHILE can be used here as it is used to show contrast. 3 gives us the cause for the poor health of Spain. Both AS and SINCE can be used here to show causation. 3 and 1 & 3 and 2 can be used here, out of which only the latter is given in the options. The joined sentence will be: "Students expressed concern about whether their college education would be worthwhile and whether they would find a job that matched their skills and level of education, while others shared that the large number of young people leaving Spain to find jobs elsewhere in Europe threatens the health of Spain since it already faces lower birth rates and an increasingly aging population." Thus, (b) is the right answer.