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Here are the combined sentences using relative clauses: 1. She has asked you the question three times, which you can still not understand. (Alternative: She has asked you the question three times, but you still can't understand it.) 2. The street that leads to my school is very nice. (Alternative: The street, which leads to my school, is very nice.) 3. The doctor, whom you spoke to yesterday, isn't here today. (Alternative: The doctor to whom you spoke yesterday isn't here today.) 4. My brother, whom you talked to at my birthday party, wants to meet you. (Alternative: My brother, who you talked to at my birthday party, wants to meet you.)