Why were you late for class this morning?I was delayed by()

题目

Why were you late for class this morning?I was delayed by()
a heavy traffic,heavy traffic,some heavy traffic,traffic being heavy.应该选哪个?

答案

应该是
I was delayed by (heavy traffic)
heavy traffic 前不加冠词
这是习惯表达方式.
比如
Heavy traffic has caused chaos in the city
你只要网上搜索就知道这是正确的说法.