Fill in the blanks with the most appropriate option:-

I have not ________ anything today.

eaten

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

The sentence "I have not eaten anything today" is in the present perfect tense, which is used to talk about an action that started in the past and is still happening now. The other options are not as appropriate.

• Eating is the present continuous tense of the verb "to eat". This does not make sense in the context of the sentence, as the speaker is not talking about an action that is happening now, but an action that did not happen.
• Ate is the simple past tense of the verb "to eat". This does not make sense in the context of the sentence, as the speaker is talking about an action that did not happen today.
• Eat is the infinitive form of the verb "to eat". This does not make sense in the context of the sentence, as the speaker is not talking about an action that did not happen, but the lack of an action.