by investing in U.S. firms that do business in China you are not ignoring it
We are talking about index funds. I don't think a US equity index will give you any meaningful exposure to specifically China (as opposed to, say, some global factor like risk appetite).
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.