阅读下面材料，在空白处填入适当的内容（不多于3个单词）或括号内单词的正确形式。
If you put a buzzard（秃鹰） in a pen（围栏） six to eight feet square and     (entire) open at the top, the bird, in spite of its ability to fly, will be a prisoner．The reason is       a buzzard always begins a flight from the ground with run of ten to twelve feet．Without space to run, it will not even attempt to fly,       remain a prisoner for life in a small prison with no top．
The ordinary bat, if       (place) on the floor or flat ground, all it can do is to move slowly about helplessly and, no doubt, painfully, until it reaches some slight    (high) from which it can throw itself into the air. Then, at once, it takes off like a flash．
A bumblebee （大黄蜂）, if dropped into an open glass, will be there       it dies, unless it is taken out．It never sees the means of escape at the top, but insists on   (try)to find some way out through the sides near the bottom．
   many ways, there are lots of people like the buzzard, the bat and the bumblebee．They are struggling about with all their problems and frustrations, not      (realize) that the answer is right there above them．