Olga, "Whenever" used as a conjunction has two meanings. whenever....any time when (when and if) -You can leave, whenever you want...... в любое время, когда захочешь whenever.....every time that. -In Petersburg he takes his umbrella, whenever he leaves the house...каждый раз, когда If you look at the question logically, there are two clauses. 1) They are going to leave the area 2) they sell their house. Usually people leave the area AFTER they sell their house. "When" and "whenever" can be used to refer to the future, thus "They're going to leave the area whenever they sell their house." means they are going to leave the area in the future when (after) the house is sold. This is probably the answer the author of the test is looking for. These tests can be confusing even for native speakers. Often you can find a context where both answers are correct, especially if you have an advanced knowledge of the English language, and become a victim of overthinking. умничание By the time....not later than a specified time; BEFORE, at, ON, or in a specified time. "They are going to leave the area BEFORE they sell their house." This is not the usual order of events, but this statement could make sense as a prediction, because we don't know when they will sell their house. -A fortune teller, after reading her cards, declares. "They are going to leave the area by the time they sell their house." -You know that they have been trying to sell their house for a long time without sucess, so you predict, "They are going to leave the area by the time they sell their house." "They're going to have left the area by the time they sell their house." Use of the future perfect emphasizes that they will leave BEFORE the date of the sale, not ON the date of the sale. The choice with BY THE TIME makes sense if you add additional context; however, there can only be one answer, and logic points to WHENEVER as the correct choice.

When and whenever are possible. In the case of whenever, it means that they have decided to move, but have not settled on a date and are going to let the sale of the house dictate when they actually do it.

Actually, both are fine, but whenever is better. While your definition of whenever is correct, whenever also means "when", but said emphatically. In this case, it can imply that the point in time at which they will sell their house is quite unknown. As for by the time, this means, before or at the exact same time as. So, while "They will have left the area by the time they sell their house." or "They will leave the area by the time they sell their house." are both more typical statements, "They are going to leave the area by the time they sell their house." also works if the two happen at the same instant in time. Having said all of that, "They are going to leave the area whenever they sell their house." is the correct choice, remembering that in this case "whenever" just means "when".

Olga, you are absolutely right in your use of "they're going to have left" if using "by the time"! So, whenever is the only right answer here, although where I live, in the US, people would probably use "when" rather than "whenever" in this sentence. I actually find this use of whenever to be a bit odd, for the reason that you mention...after all, they are only selling one house and leaving one time, and the word whenever does imply repetition! I like it better in a situation like this, in which the event is repeated: They are going to leave the area whenever they rent out their house to a group of tourists.

First we must understand the meaning of the sentence. The sentence can mean two things as follows : 1. when they sell the house, as a result, they will have to leave the area (maybe because they don't have any other place to live in). So the correct sentence would be : They are going to leave the area WHEN they sell their house. As you said correctly, whenever doesn't quite fit the bill. However, here Whenever is used as "when ever", that is at the time when they sell the house. However, still "When" is a better and more natural word to use. 2.) There is a context in which "by the time" may actually make sense. e,g, A. They don't have much time. The authorities have asked them to leave the area as soon as possible. But they are finding it hard to find buyers for their house. B. They are going to leave the area by the time they (are able to) sell their house. (means in the time they will take to sell the house) A. Yes. The house won't sell so easily looking at the condition it is in.