阅读下面短文，在空白处填入一个适当的词，或填入括号中所给单词的正确形式（每空不多于3个单词）。
Long ago there lived a kind old man. One day while walking through the woods, the old man found a butterfly's cocoon(茧). He took ____ home. A few days later, a small opening appeared. He sat and watched the butterfly ____ several hours as it struggled(挣扎) to force its body through that little hole.
Then the nice man decided ____ (help) the butterfly, so he cut the remaining bit of the cocoon. The butterfly then came out ____ (easy). But it had a fat body and small, shriveled(皱缩的) wings. The man continued to watch the butterfly because he expected that, at any moment, the wings would enlarge and expand to be able to support the body ____ would grow small in time. However, neither happened. In fact, the butterfly spent the rest of its life ____ (lie) with a fat body and shriveled wings. It was never able to fly.
What the man did not understand was that the struggle was a must for the butterfly to get through the tiny opening. That's the ____ (nature) way of forcing fluid(营养液) from the body of the butterfly into its wings.
In this way, it would be ready for flight when it achieved its freedom from the cocoon. Sometimes struggles are exactly ____ we need in our life. If we ____ (allow) to go through our life without any ____ (difficult), it will weaken us. We won't be strong as what we could have been. And we can never fly.
