【正确答案】Part-time jobs are very useful for full-time students because they can not only earn money but also gain career experience．

【答案解析】汉语原句中虽然没有明显的逻辑连接词，但翻译成英语时加上隐藏于前半句和后半句之间的表示因果关系的because句义才完整。