Although his lawyers were optimistic, they couldn't be sure about the final outcome of the trial.尽管他的律师持乐观态度，但对于最后的判决结果，他们也不太有把握。It is impossible to be sure about the value of land.土地的价值是无法确定的。I think children are influenced by these films, but it's impossible to be sure about this.我认为儿童会受到这些电影的影响，但是没法确定。