It is hard to imagine what this place looked like twenty years ago.
考点:困难的:hard;想象:imagine
句子结构:It's hard to do sth.:很难做某事。“想象“后边是一个完整的句子,所以要用从属连词引导宾语从句。“是什么样子”可以用what代替,并且作连词引导从句。