英语四级作文常用句型：基本原因

　　基本原因 ——分析某事物时, 用此句型说明其基本的或者多方面的原因.

　　[1]. The answer to this problem invovles many factors. For one thing... For another...... Still another ...

　　[2]. A number of factors , both physical and psychological affect .... /both individual and social contribute to ....