Singular-plural alternation. Having said that, I feel it really is a similar style of phenomenon. Semantics is stepping in and influencing the verb settlement — it's actually not generally a purely syntactical determination. 知乎，让每一次点击都充满意义 —— 欢迎来到知乎，发现问题背后的世界。 The subject of the sentence "Is either of you free?" is "possibly" not "you" https://sexeslive.com/