I found unit 3 to be the most interesting because I like animals.

问题描述:

I found unit 3 to be the most interesting because I like animals.
我发现第三单元最有趣,因为我喜欢动物.
found(过去式)...to be...这个结构我感觉有点怪.
可以这样说吗:I found unit 3 the most interesting because I like animals (就像:I find it difficult to...

可以,I found unit 3 the most interesting和i find(found) it (unit 3) difficult (the most interesting)结构完全一样的.
find it to be也是可以的.