Question

1. if an astronaut travels to the international space station, ____ will conduct research there.

c. they
a. our
d. he or she
b. it

Explanation:

The subject "an astronaut" is singular and gender - neutral. "They" as a singular pronoun has become more accepted in modern English, but traditionally, "he or she" is used to refer to a singular, gender - neutral antecedent in formal language. "Our" is a possessive pronoun and not a subject pronoun. "It" is used for non - human or animal subjects. "They" as a singular can be informal in some contexts.

Answer:

d. he or she