________ several times, but he still doesn't know how to do it properly．
A.Being shownB.Having shownC.Having been shownD.I've shown him在线课程D
解析：
考查谓语动词和非谓语动词的区别。根据题干中的but可知这是一个由转折连词连接的两个句子，因此要选谓语动词而不选非谓语动词。本题中如果去掉but则答案为C。