let down的意思？

let down的音标：let down的英式发音音标为：[let daun]let down的美式发音音标为：[lɛt daʊn]...

Sadly, the film is let down by an excessively simple plot.遗憾的是，过于简单的情节使得这部电影差强人意。He let down the tailgate so the dog could jump out.他放下后背门，好让狗跳出来。But then to be let down like that, oh it's so unfair!但是接下来竟让人如此失望，唉，这...