Helen is working _the physics problem._上为什么是填on,而不是at/out/over?今晚必须有回答！谢

I'm hard-working,helen is hard-working too,合并为一句[ ]helen and I[ ]hard-working. Helen's parents working in China,her father is a teacher and her mother is a lawyer,Helen was born in the United States.翻译上段话 My name is Helen.针对“Helen”提问 This is Helen. Helen is working _the physics problem._上为什么是填on,而不是at/out/over?今晚必须有回答！谢 Helen is Russian.(划线部分提问）填：( )( ) is Helen? she is his sister,helen. My name is Helen.翻译 Helen ,name ,her ,first ,is Helen is good()English.快 Sally is ------- ------- taller than Helen. This is Helen中文怎么说 Helen is fine（特殊疑问句) This is Helen's present划线提问 Helen's 划线 That is Helen ’s green blouse对Helen’s提问 helen.is.one.of.millies.best.friend对helen提问 Helen is fine.(对画线部分提问) Helen? Who is__(thin),you or Helen?Helen is.