While previous and recent etiological analyses remain non-conclusive, environmental factors were shown to be associated with BN.
虽然前期和最近的病原分析不具决定性，但是环境因素却显示出同树皮坏死有联系。
2
D. C. and A. C. characteristics of non-ideal operational amplifiers are examined from a general viewpoint, and a set of useful expressions and conclusive results are obtained.