Which one of the following sentence is a proposition? (1) 4+7=12 (2) What are you doing?(3) 3n ≤81, n∈N(4) peacock is our national bird. (5) How tall this mountain is!

Which one of the following sentence is a proposition?
(1) 4+7=12
(2) What are you doing?
(3) $3^{n}$ $\leq$ 81, $n \in N$
(4) peacock is our national bird.
(5) How tall this mountain is!

Gap-fill exercise

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