1. that's a clear signal that the admission committee don't really care too much about previous publication and thus there are only 1 space for writing sample.
what I suggest to do is to attached the completed one (论文最终稿) as writing sample, and the one in progress as 辅助材料 if possible (if not then just state the link / number in CV, no one cares anyway)
2. means that how much the 导师 are willing to recommend you in the application. Just writing a normal reference letter? writing an impressive one? or even talk to the faculty of the department you had applied in person? This makes a huge difference.