The correct answer is D. no article.
The word “piano” is a common noun, which means it refers to any piano in general. We do not use articles with common nouns unless they are specific or unique. For example, we would say “I play the piano” if we were talking about a particular piano that we own or are familiar with. However, in the question “Can you play piano?”, the piano is not specific or unique, so we do not use an article.
The other options are incorrect because they are all articles. Articles are used to specify which noun we are talking about. For example, we would say “I play a piano” if we were talking about any piano, or “I play the piano” if we were talking about a particular piano that we own or are familiar with. However, in the question “Can you play piano?”, the piano is not specific or unique, so we do not use an article.