Answer:
number 4 is the correct answer
The husband gets tickets to a rich person's party, worries about getting a new dress, borrows jewelry, goes to party, loses necklace, works for ages, buys necklace, meets friend and finds out the necklace is fake.
The sentence in which the underlined infinitive phrase functions as a subject is the last one - to quickly move large groups of people is the purpose of public transportation.
<em>To quickly move </em>is the infinitive phrase, and it is a subject.
C: Because he made significant discoveries about electricity,
