Hi Mary, “He was the pioneer of Russian sculpture and a master of exceptional talent.” For the first part of the sentence, you can use ‘a’ or ‘the’, depending on your meaning. If he is considered to be the one and only pioneer of Russian sculpture, then you would use ‘the’. If he was only one of the pioneers, but there were several or many pioneers, then you would use ‘a’. For the second part, you would use ‘a’ because he is not the only master artist. I hope this is helpful! :)