The correct answer is: A. I warned him to be careful as the steps were very slippery.
The sentence “Be careful; the steps are very slippery” is a warning. A warning is a statement that tells someone to be careful or to avoid something dangerous. In this case, the speaker is warning the listener to be careful because the steps are very slippery.
The sentence “I warned him to be careful as the steps were very slippery” is a complete sentence that expresses the same meaning as the original sentence. It is grammatically correct and uses the correct verb tense.
The sentence “I warned him to be careful as steps were very slippery” is not a complete sentence. It does not have a subject or a verb.
The sentence “I told him to be careful and steps were very slippery” is not a complete sentence. It does not have a subject or a verb. It also uses the wrong verb tense. The verb “told” is in the past tense, but the sentence is about something that is happening in the present.
Therefore, the correct answer is: A. I warned him to be careful as the steps were very slippery.