"The table is long."
その means the thing that the counterparty was talking about. Not necessary referring to the actual position of the thing. So it means the definitive "the" in English.
Yes その would mean "the" in this context, but "the" doesn't necessarily translate to その.
テーブルが長いです was marked wrong in favor of テーブルは長いです。To me, the first means "the table is long" and the second means "tables, in general, are long." I know they were looking for その or something, but that wasn't included in the "correct" answer.
yea :( I felt like テーブルが長いです is the right answer too, wouldn't it be the same thing as そのテーブルは長いです? Can someone feel for the nuances between the two?
テーブルが長いです and テーブルは長いです both means in general tables are long or some table is long. (Note that I am not talking about universal facts, just in contrast to a particular object.)
Now, the difference between は and が in this case is that,
テーブルは長いです A simple description of a table or multiple tables. In this case "the table is long" means "some table is long." We know there is a table. The important information we get from the sentence is "long." The table is not short/thin/tall. The table is long.
テーブルが長いです It implies that a table is long, but not other things. Something is long there, not the chair/TV/carpet. The table is long. We know there are something is long and we learn that it is some table that is long.
そのテーブル makes the table a particular one vs テーブル only. The particular table can be a physically near one or logically near one, where it can refer to a table discussed earlier in the conversation. To summarize
そのテーブル can mean a particular table physically near the listener but further from the speaker. In this case, "that" table is used.
そのテーブル can mean a table introduced in the conversation, like "There is a table in the conference room. The table is long." We use そのテーブルは長いです.