Can a ameba become large enough to eat a city?

No, an amoeba cannot become large enough to eat a city. Amoebas are single-celled organisms typically measuring only a few micrometers in size. Even the largest known amoebas, like the giant Amoeba proteus, are still microscopic and cannot grow to a size capable of interacting with objects like buildings or cities. Their feeding mechanisms rely on engulfing smaller organisms, which is not feasible on a large scale.