Scientists can only suppose that the illness is caused by a virus.科学家们只能推测这种疾病是由一种病毒引发的。I can only surmise that this happened last week.我只能推测这件事发生在上个星期。We can only surmise and prophesy.我们只能推测和预言。We don't know why the prehistoric stone circles were built. We can only speculate.我们不知道建造史前巨石圈的原因,只能推测。