The correct answer would be: Her hat was blown off by a strong wind.
Passive voice is frequently used and it is most often used in formal texts, but it is also used everyday. When we use passive we focus on the object or a person that experiences the action not the one that performs it. Passive voice is formed by using the correct form of the verb to be plus past participle.
They explain that maintaining a life in the desert is difficult.
Im pretty sure that your answer is going to be A.) Because it's important to know outside information about every topic.