Ex91. (+) am doing(-) I am not doing ...(?) Are you doing...?Yes, I am/ No, I am not2. (+) is making(-) ...isn't making...(?) Is Tim making...?Yes, he is/ No, he isn't3. (+) is writing(-) ...isn't writing...(?) Is Mai writing...?Yes, she is/ No, she isn't4. (+) are painting(-) ...aren't painting...(?) Are Lan and Ba painting...?Yes, they are/ No, they aren't5. (+) are playing(-) ...aren't playing(?) Are the boys playing...?Yes, they are/ No, they aren't Câu trả lời: Ex91. (+) am doing(-) I am not doing ...(?) Are you doing...?Yes, I am/ No, I am not2. (+) is making(-) ...isn't making...(?) Is Tim making...?Yes, he is/ No, he isn't3. (+) is writing(-) ...isn't writing...(?) Is Mai writing...?Yes, she is/ No, she isn't4. (+) are painting(-) ...aren't painting...(?) Are Lan and Ba painting...?Yes, they are/ No, they aren't5. (+) are playing(-) ...aren't playing(?) Are the boys playing...?Yes, they are/ No, they aren't