下面这个英语句子有什么错误啊?

I was visiting the zoo on that afternoon when I heard bears roaring terriblely.

把on that afternoon 改为in that afternoon, 因为介词搭配是用in ，比如 in the morning 等，而用on 是on that day 等具体日期。

I was visiting the zoo (in) that afternoon when I heard bears roaring terriblely.

I was visiting the zoo (in) that afternoon when I heard bears roaring terriblely

句型 念起来拗口 感觉不对 也就是语感不好 问题出在最后一个单词terribly 让整个句子的结尾很重 感觉句子还没结束 后面还得跟点什么 而且bear roaring总是比较terrible的 所以terribly可以省略

另外 on the afternoon后面应该有具体的日期 所以这里要用(in) the afternoon

可以把句子改成：
1/ I was visiting the zoo that afternoon when I heard the bears roaring.

如果要保留terribly,此句可以这样：
2/I was visiting the zoo that afternoon when I heard the terrible bears'roaring.

这样的话 句子就有平衡了 visit the zoo(n.动物园）对应 hear the roaring (n.吼叫）

或者：
3/I was visiting the zoo that afternoon when I heard the bears roaring, which was so terrible.