86．In 15 or 30 seconds．a speaker cannot establish the historical context that shaped theissue in question，cannot detailthe probable causes of the problem，and cannot examine alternative proposals to argue that one ispreferable to others．

(以and连接的并列句)

在15或30秒的时间里，发言人无法建立形成正在讨论的问题的历史背景；不能详细阐述问题产生的可能原因；无法仔细审查几种建议以辩论哪一种更可取。

解析：

主句1：a speaker cannot establish thehistorical context

主句2：cannot detail the probable causesof the problem

主句3：and cannot examine alternativeproposals

从句1：that shaped the issue in question

从句2：to argue that one is preferable toothers．

主句1，2，3并列关系

从句1修饰主句1中的context

从句2修饰主句3的proposal