What requirements should be met for manhole pit backfilling?

The backfill soil of manhole pit is forbidden to be higher than the elevation of manhole ring. a、 100； 300 B、 150； 250 200; 300D、250； 300 Remarks: There must be no hard objects such as gravel and brick with a diameter greater than 100mm in the backfill near the manhole wall. Manhole pit shall be buried 300mm at a time, and it shall be strictly compacted. Backfilling of manhole pit is strictly prohibited to be higher than the elevation of manhole ring. Correct answer: A failed to get 0.0 on this question. The elevation of the top of manhole ring shall comply with the design regulations, with the allowable positive deviation not greater than mm, and there shall be an oral cavity not less than mm between the orifice ring and the upper complex. The overlap between the oral cavity and the upper compound should be smeared with eight characters, and the nozzle ring should be intact. A, 10 15C, 20 D, 25 remarks: the elevation of the top of manhole ring should comply with the design regulations, and the allowable positive deviation is not more than 20 mm. An oral cavity of not less than 200mm should be established between the orifice ring and the upper tooth complex. The overlap between the oral cavity and the upper compound should be smeared with eight characters, and the nozzle ring should be intact. Correct answer: there is no 0.0 point for this question C. The number of steel bars, binding and concrete covered on manhole shall meet the design requirements.