Which sentence has an infinitive or infinitive phrase that functions as a direct object?
to see their work, visit the campgrounds in death valley.
because of the great depression, these men needed to work.
their first task was to build barracks and other permanent structures.
in 1933, legislation was passed to establish the civilian conservation corps.

The correct option is B. Because of the Great Depression, these men needed to work. The infinitive phrase here that functions as a direct object is to work. The easiest way to find out what the direct object is is to ask the question - What? So, what did these men need? To work. Furthermore it could be replaced by the word "it".

A direct object is a noun phrase denoting a person or thing that is the recipient of the action of a transitive verb.

c.to compare several aspects of the tragedy to other worldwide tragedies

the answer is the second one.