问答题 翻译：She purchased a used computer for￥3500 on credit by making a ￥1500 cash down payment and obtaining two－month accounts payable for the remaining￥2000.

问答题 翻译：She purchased materials of￥4000 in cash.

填空题 用二苯胺磺酸钠作指示剂，用Ce4+滴定Fe2+，突跃为0.86V~1.26V，加入磷酸后，突跃为（）。