Select the abbreviation that tells how the italicized noun clause is used.
s-subject, do-direct object, sc-subject complement, op-object of preposition
i am optimistic enough to believe that young people will respond to a challenge.
s
op
sc
do

The abbreviation that tells how the italicized noun clause is used is DO. The fourth option is correct.

The clause: "that young people will respond to a challenge" is a direct object. This clause cames right after the verb believe which is a transitive verb which requires a direct object to conve a compkete thought that makes sense.

The direc object is a noun phrase denoting a person or thing that is the recipient of the action of a transitive verb

chapter i -- paris: september, 1792

a surging, seething, murmuring crowd of beings that are human only in name, for to the eye and ear they seem naught but savage creatures, animated by vile passions and by the lust of vengeance and of hate.

during the greater part of the day the guillotine had been kept busy at its ghastly work: all that france had boasted of in the past centuries, of ancient names, and blue blood, had paid toll to her desire for liberty and for fraternity.

hope this answer you: )!