阅读下列材料，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。
    Friends are very important to teenagers．They not only give fun and excitement to each other but____give advice to one another．They can talk about lots of problems with the friends．As for parents，they are____(sure)important but some teenagers often say their parents don't understand them．In large families，brothers and sisters often argue____each other for good things，such as delicious food or super toys．So most teenagers think friends are____(important)people in their____(life)．