Len was thirty years old, and he had very long hair, He lived in a big city, but one year he did not find any work there, so he went to a small town and began looking for work there. He went to a lot of places, but nobody wanted him.
Then he met an old friend, and this man said to him, “People in this town don’t like long hair. Why don’t you go to a barber (理发师) ？ He can cut a lot of it off and then you can get some work..”
Len went to a barber and said, “Please cut most of my hair off.” The barber began. He cut and cut for a long time and then he said to Len , “Were you in the army a few years ago?” “Yes, I was.” Len answered. “Why did you ask that?” “Because I have found your cap,” the barber answered.
小题1:Len was twenty years old.
小题2:Len had very long hair.
小题3:Nobody wanted Len for work.
小题4:Len met an old classmate.
小题5:The barber cut off a lot of Len’s hair.
的两个焦点F1和F2上放置两个频率相同的波源，它们激起的波的波长为4cm．就图中A、B、C、D四个质点的振动，下面说法中正确的是（ ）