The correct answer is A. 21543.
The first word is “am”, which is the first person singular present tense of the verb “to be”. The second word is “playing”, which is the present participle of the verb “to play”. The third word is “now”, which is an adverb that indicates the present time. The fourth word is “I”, which is the first person singular pronoun. The fifth word is “hockey”, which is a noun that refers to a game played on ice with a puck and sticks.
The sentence “I am playing hockey now” is a simple sentence that consists of a subject, a verb, and an object. The subject is “I”, the verb is “am playing”, and the object is “hockey”. The sentence is in the present tense, and it indicates that the speaker is currently playing hockey.
The other options are incorrect because they do not form a grammatically correct sentence. Option B, 51423, is not a sentence because it does not have a subject. Option C, 45231, is not a sentence because it does not have a verb. Option D, 41253, is not a sentence because it does not have a subject or a verb.