The bulidings have been designed by Kurt Gunter为什么用完成时

The bulidings have been designed by Kurt Gunter为什么用完成时 the buildings have been designed by sb. the software have been explicitly designed for use by outsid Mobile homes,pulled by specially designed trucks have been i have been designed the buildings have been so well designed amd bui 但为什么This is my first time to have been here.里要用完成时?谢谢~~ 英语翻译They have in large part been designed and driven by what the new suspension bridge(had been designed)by the end of la how long have you been like this?为什么用完成时态?请类似的举例 英文好且懂物理的来The Corpus Clock has been invented and designed by i have arrived by train中的arrive 为什么用完成?而不用be there?