20．________ I understand you，I still can’t support you.

A．When　　　　　 B．After　　　　　　 C．While　　　　　　 D．As

19．________ to the Qin Dynasty，the traditional crosstalk shows have made people roar with laughter.

A．Dating back　　 B．Dating from　　　　 C．Dated from　　　 D．Dated back