《关于进一步深化电信基础设施共建共享 促进“双千兆”网络高质量发展的实施意见》指出，各地、各企业在行业内深化共建共享的同时，也在推进与电力、市政、交通运输等领域的跨行业基础设施共享，但（）等问题，增加了跨行业共享的工作难度。

问答题if a monopolist has zero marginal costs, A. it will produce the output at which total revenue is maximised. B. it will produce in the range in which marginal revenue is still increasing. C. it will produce at the point at which marginal revenue is at a maximum D.it will produce in the range in which marginal revenue is negative

问答题以下是破伤风内毒素给药的禁忌