Translation:The seas beside the cities are cold.
In Hungarian "tenger" and "óceán" are really different in usage. "Tenger" is a kind of so-called inside-a-continent water I mean it is partly or fully enclosed by land. For example Adriatic sea, Black sea, Caribbean sea, Chinese sea and so on. An ocean ("óceán") is between continents, its area is some ten millions square kilometres and its average depth is some thousand meters and also it has an own flow system like the Gulf Stream in case of the Atlantic Ocean. We know only five oceans like the Atlantic, Pacific, Indian, Southern (Antarctic) and the Arctic Oceans. As far as I know the word "sea" is often used interchangeably with "ocean" in American English.
Literally, "sea" = "tenger" and "ocean" = "óceán".
But there may be some difference in usage. Generally speaking, English may prefer saying "oceans" when talking about large bodies of water in general (not sure about this but that is my feeling), while Hungarian uses "tengerek" for this purpose.
My answer "the seas are cold besides the cities" was rejected. The 'correct' solution by DL would be "the oceans are cold beside the cities". Both translation should be acceptable.