i heard 是主动,“我听到” i was heard是被动,"我被听到”
(1)when 即可表示时间点也可表示时间段.从句谓语动词可以是延续性的,也可以是非延续性的.如：When he was a child he was always trying out new ideas.他小时候就常常试验一些新的设想.
(2)while只能表示某个时间段,从句谓语动词只能是延续性的.
如：While Jim was mending his bike,Li Ming csme to see him .正当吉姆修自行车时,李明来看他.
(3)while 引导的时间状语从句多用进行时,而when 引导的时间状语从句多用一般时态