在数学中,为了书写简便,18世纪数学家欧拉就引进了求和符号“https://bgk-photo.cdn.bcebos.com/5882b2b7d0a20cf48ccd6fbf66094b36acaf9975.jpg”.如记https://bgk-photo.cdn.bcebos.com/f3d3572c11dfa9ecff2dc77772d0f703918fc14b.jpg,https://bgk-photo.cdn.bcebos.com/42166d224f4a20a4c01dada780529822720ed04b.jpg;已知https://bgk-photo.cdn.bcebos.com/d4628535e5dde711458fd296b7efce1b9d166175.jpg,则m的值是……………………( )A、40B、- 70C、- 40D、- 20