Question 10:

Correct answer: A. fastened
Explanation: The context requires a past participle form of the verb "fasten" to complete the sentence. "Fastened" indicates that the seatbelt should be in a fastened state while seated.
Question 11:

Correct answer: C. Should
Explanation: The sentence expresses a conditional situation: "If the seatbelt sign comes on again, you should return to your seat." "Should" is used to express obligation or advice in such cases.
Question 12:

Correct answer: D. are not protected
Explanation: The sentence refers to the toilets, which are plural. Therefore, the verb "are" is used with the past participle "protected" to indicate that the toilets are not protected from smoke detector alarms.