单项选择题 云计算可以认为包括以下几个层次的服务：基础设施即服务（IaaS），平台即服务（PaaS）和软件即服务（SaaS）。A.对B.错

问答题 现阶段电动汽车的主流动力电池类型分为(____)、(____)、(____)、(____)四种。

单项选择题 If the feed is introduced at one point along the column shell, the column is divided into an upper section, which is often called  the stripping section, and a lower section, which is often referred to as the rectifying section.