回複：請問在北京簽證可以用從網上下載的DS156，157表嗎？謝謝

You can use the DS156, DS157 downloaded from the web and it is NOT required to be copied two sided. I just did it recently. Try to fill the DS156 form on the internet and then print the form. This way, you will get a barcode at the third page, which will cut your waiting time once you are inside the embassy, since they already have a kind of record of you.