What a beautiful day it is.
Choose the option that best corrects the underlined word.

We observe that the given sentence is exclamatory in nature because of its construction. However, it uses an incorrect punctuation. allow us to analyse the given options so as to seek out the right punctuation.
> “Is?” uses a matter mark. a matter mark is employed at the top of an interrogative. An question is employed to ask questions.
For example: Is she okay?
We observe that it doesn't fit the context of the given sentence. Hence, we are able to say that option ‘a’ isn't the right answer.
> “Is!” uses an exclamation point. An punctuation is employed at the top of an exclamatory sentence. An exclamatory sentence is employed to specific a powerful emotion.
For example: How reasonably you!
We observe that it fits the context of the given sentence. Hence, we will say that option ‘b’ is that the correct answer.
> “Is...” uses ellipses. Ellipses is employed to convey that the sentence has been left incomplete.
For example: I don’t really know what to mention to the present but…
We observe that it doesn't fit the context of the given sentence. Hence, we are able to say that option ‘c’ isn't the proper answer.
> None of the above isn't a sound answer as option ‘b’ is that the correct answer.
Hence, we are able to conclude that option ‘b’ - “is!” is that the correct answer.