how can one distinguish in Swahili between ''a" and "the"? I was marked wrong for sayng "the market" instead of "a market" just because you had decided that "a' was correct.
Well, most of the time when there's an issue like this, it's just because the course creators were pressed for time and made a lot of errors and inconsistencies.
But in this case "There is the market" just isn't as natural. It does sometimes happen, such as when you're reminding someone of the existence of a specific market, or if you're going to give more information about a specific market, but most of the time when you use "there is" or "there are", you're stating the existence of something that you're introducing for the first time, so it's indefinite.
I would say, for example:
Soko lipo. =
The market is there. (We were already talking about the market).
Kuna soko. = There is
a market. (I'm telling you about the things that exist.)