She is preparing . . . . . . . . speech for tomorrow.

The correct answer is A. a.

The article "a" is used before singular nouns that refer to a general or indefinite thing. In this case, the speaker is preparing a speech for tomorrow, but we do not know what the speech is about. Therefore, we use the indefinite article "a".

The article "an" is used before singular nouns that begin with a vowel sound. In this case, the noun "speech" begins with a consonant sound, so we do not use "an".

The article "the" is used before singular nouns that refer to a specific or definite thing. In this case, the speaker is preparing a speech for tomorrow, but we do not know what the speech is about. Therefore, we do not use "the".

The answer "none of the above" is incorrect because the speaker is preparing a speech for tomorrow. Therefore, we need to use an article.