Quiz on heaps doubt

#1

In what best time complexity you can merge two max-heaps? (Assume size of first heap is (m+n) and the second is (n))
This is question in quiz. I marked the answer O(m+n) but it is showing wrong answer and saying the correct answer is O(1). Please explain it in detail.

#2

@Kajal Answer must be O(m+n).You are correct.It must be marked wrong. I will report that.

#3

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