专八改错 The shops are overstocked with food not only as there is more food available,but also

题目

专八改错 The shops are overstocked with food not only as there is more food available,but also
because people,frightened by high prices,are buying less of it.参考答案是将as 改为because.请问这是为什么?

答案

“商店里面充斥的食品：这不仅是因为有更多食物可供选择,而且还因为害怕的高价格的人们购买少了.”
as:由于,鉴于.主从并重,从句说明原因,主语说明结果.通常放在句首
because:因为.表直接原因,回答why的提问;一般放在主句之后,也可单独存在.