Answer and Explanation:
Even though this question is missing the instructions, we can assume it is a "fill in the blanks".
<u>The sentence is missing a verb. Due to the position of "usually", we can say the verb that is missing either the verb "be" or a modal verb </u>- main verbs would come after "usually", not before. <u>Since there is no other verb in the sentence, we can eliminate modal verbs and choose verb "be" as the best option.</u> Modal verbs need another verb to complement their meaning; the verb "be", in its turn, can work on its own.
<u>The subject is compound, joined by "or". In this case, the verb agrees with the part of the subject that is closest to it.</u> <u>Since "attendant" is singular, the verb will also be singular.</u> Therefore, the correct sentence would be:
- The pilot or flight attendant is usually alert during the flight.
