The correct answer is: B. We use this house very rarely.
The sentence “This house is used very rarely by us” is in the passive voice. The passive voice is used when the focus of the sentence is on the action, rather than the person or thing doing the action. In this case, the focus is on the fact that the house is used very rarely, not on who is using it.
The verb “use” can be used in both the active and passive voice. In the active voice, the subject of the sentence performs the action. For example, “We use this house very rarely.” In the passive voice, the subject of the sentence receives the action. For example, “This house is used very rarely by us.”
The other options are incorrect because they are not in the passive voice. Option A, “We are using this house very rarely,” is in the present progressive tense. Option C, “We used this house very rarely,” is in the past tense. Option D, “We uses this house very rarely,” is incorrect because the verb “use” does not take an “s” in the third person singular.
In conclusion, the correct answer is: B. We use this house very rarely.