Two men were sitting______at a bar at the top of the Empire State Building.空格填什么还有原因~

选A .现在分词的一个功能,就是充当“伴随状语”.一个主要动作进行时,另一个动作也在进行.一主,一次,两个动作,谓语动词是主要动作,另一个次要动作,就用伴随状语表达.
另例：They went to the park together,singing all the way.我看到有一个版本的答案选C，百思不得其解，这个没有逗号的句子也能用ing表达伴随状语吗？先说C。从语法（理论上）看，drunk 做伴随状语是可能的。但是从语义逻辑上分析：二人正坐在酒吧醉了，似乎不如：二人正坐在酒吧喝酒，更合乎逻辑。 再说没有逗号的问题。没有逗号的句子，似乎也没有什么错误。如果是人家原著这么写的，咱们也不能说人家写得不好。但是，如果我们自己写句子，尽可能做到清晰、漂亮。如果是我，我会这样表达：Two men were sitting at a bar at the top of the Empire State Building，drinking while talking heartily. 或者：Two men had been sitting at a bar at the top of the Empire State Building and both of them were quite drunk by now.