下面的段落摘自 2017 年高考英语的浙江卷读后续写：

Mac was pedaling hard now. He waved and yelled at passing cars but was careful not to slow down. He saw a steep uphill climb before him. He knew that once he hit the hill, he’d be easy caught up and the wolf’s teeth would be tearing into his flesh. 

对划线部分的 be easy caught up 有疑问，为什么不用 easily？虽然 easy 也可以用作副词，但书上说，它的副词用法是很有限的，能这样用吗？