题目7单选题
用草酸钠作基准物标定高锰酸钾标准溶液时,开始反应速度慢,稍后,反应速度明显加快,这是( )起催化作用A. 氢离子B. <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201808/7fe74233e67f440c911825d98db4a360.png">C. <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201808/dbee2762f99c4a6d8555fa5db2ed7398.png">D. <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201808/47f2dc7bcbd14ac29a3b2ed20f706189.png">