1、过去完成时表示“过去的过去” “had +动词的过去分词”构成, had通常用于任何人称。Bythetimehewastwelve,Edisonhadbegantomakealivingbyhimself.Mostoftheguestshadleftwhenhearrivedattheparty.Most of the guests had left when he arrived at the party. Whenthepolicearrived,thethieveshadrunawayHehadworkedfor4yearsbef