Foundation
English
Tenses
Sentences
Transformation of Sentences
Question
Convert the given statement into a yes/no question:
(Ensure that the meaning of the sentence remains unchanged.)
Mary has been studying all night.
Has Mary been studying all night?
How long has Mary been studying?
Does Mary study all night?
Will Mary be studying all night?
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Solution
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'Yes/No' questions are those questions which start from helping verbs like was, are, were, is, etc. 
In such a case, the order is Verb + Subject + Object. In the given sentence, 'Has' is the verb, 'Mary' is the subject and 'all night' is the object. 
Thus, option A is the correct answer.