题目内容：

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。

An elderly teacher，with a pupil by his side，took a walk through a forest. Suddenly he_1.__(stop) and pointed to four plants close at hand. The first was just beginning to appear slowly above the ground，the second had rooted itself pretty well into the earth，the third was a small short tree，while the fourth was__2.__ full-sized tree. The tutor said to his young__3.__(company)，“Pull up the first plant. ” The boy did so eagerly，__4.__(use) only his fingers.

“Now pull up the second.” The youth obeyed __5.__ found that the task was__6.__(difficult)．

“Do the same__7.__ the third，” he urged. The boy had to use all his strength to uproot it.

“Now，” said the instructor，“try your hand with the fourth. ” The pupil put his arms around the trunk of the tall tree and couldn't even shake__8._ leaves. “This，my son，is just_9.__ happens with our bad habits. When they are young，we can remove them easily；but when they are old，it's hard to pull them out of the ground，__10.__ we pray and struggle ever so sincerely！”