A:①④
B:①②
C:②③
D:③④
—I haven't worked the problem out yet. What am I supposed to do?
—Try again! It’s only difficult.
共享单车是指企业与政府合作,在公共服务区提供自行车单车共享服务.截至去年底,中国共享单车市场整体用户数已达到18860000,这个数据用科学记数法表示为____.