He teaches us grammar.

The given sentence "He teaches us grammar." is in the active voice. To convert it into the passive voice, follow these steps:

Step 1: Identify the Subject, Verb, and Object
- Subject: He
- Verb: Teaches (present tense)
- Objects: Us (indirect object) and Grammar (direct object)

Step 2: Convert the Sentence to Passive Voice
- In passive voice, the object becomes the subject.
- The direct object "Grammar" or the indirect object "We" can be used as the subject of the passive sentence.
- The verb is changed to the passive form: am/is/are + past participle.
- The phrase "by him" is added to indicate the doer of the action.

The correct passive voice sentence is "We are taught grammar by him."