whenever When I came into the room, he was writing a letter.当我进屋时，他正在写信。
We shall go there whenever we are free.我们什么时间有空，我们就去那里。 when指的是“某一具体的时间”
whenever指的是“在任何时间”
when I was walking along the street when suddenly someone patted me on the shoulder from behind.我正在街上走着，这时忽然有人从后面拍我 的肩膀。 when意为“这时”或“在那个时候”,可以看作是并列句,这种用法的when分句一般位于句末。
while While it was raining, they went out.天下雨的时候，他们出去了。
