How can you tell if labor is scarce?

I would say in a general overview, that if workers are always being looked for to do a job, that labor is scarce. Look at welding for example, there is always a need for welders. When, in the United States, a job is vital, the government might even offer grants to get more people into the labor force, so you could tell that way.

from the conditions of the working class in england by friedrich engels,the main idea is :

the answer to your question is c