The correct answer is: D. We are taught Grammar by him.
The sentence “He teaches us grammar” is in the active voice. In the active voice, the subject of the sentence performs the action. In this case, the subject is “he” and the action is “teaches.” The object of the sentence is “us” and the direct object is “grammar.”
The passive voice is formed by using the verb “to be” and the past participle of the main verb. In this case, the passive voice sentence would be “Grammar is taught to us by him.” In the passive voice, the subject of the sentence receives the action. In this case, the subject is “grammar” and the action is “taught.” The object of the sentence is still “us” but it is now called the “indirect object.”
The progressive tenses are formed by using the verb “to be” and the present participle of the main verb. In this case, the progressive tense sentence would be “We are being taught Grammar by him.” In the progressive tense, the action is happening at the time of speaking. In this case, the action is “being taught” and the subject is “we.”
The sentence “Grammar is being taught us by him” is grammatically correct, but it is not idiomatic. In English, we do not usually use the passive voice with the progressive tenses. The most idiomatic way to say this sentence would be “We are taught Grammar by him.”