Fill in the blanks with the most appropriate option:-

Look! It _______.

is raining

The most appropriate option to fill in the blanks is is raining.

The sentence "Look! It is raining." is in the present continuous tense, which is used to talk about an action that is happening now. The other options are not as appropriate.

• Has rained is the present perfect tense, which is used to talk about an action that started in the past and is still happening now. This does not make sense in the context of the sentence, as the speaker is talking about an action that is happening now.
• Rain is the infinitive form of the verb "to rain". This does not make sense in the context of the sentence, as the speaker is talking about an action that is happening now.
• Will rain is the future tense of the verb "to rain". This does not make sense in the context of the sentence, as the speaker is talking about an action that is happening now.