To talk about an action that is still ongoing at a point in the future, we use the future perfect progressive with 'for' to emphasize the duration of the action:
By the end of September, I will have been working for the company for ten years.
In this case, the meaning of the sentence sounds similiar to one with the future perfect tense:
By the end of September, I will have worked for the company for ten years.
But what about these two sentences?
By ten o'clock, I will have been painting the house for three hours.
By ten o'clock, I will have painted the house for three hours.
I know the first sentence emphasizes the duration, as it is continuous. It's not about the completion of the action (painting).
But what does the second sentence emphasize?
Is the action (painting) completed here? Is it only about the amount of time that will have been spent on painting by ten?
I also know that the future perfect is usually used to talk about the completion of an action at a certain point of time in the future. But without 'for'
I will have painted the house by ten.
Meaning, if you come visit me at ten, the house will be painted. What about the same sentence with 'for+an amount of time'?
This is the question in a book
By the end of the day, we ....... the house for a week.
a. will have painted
b. will painted
c. have painted
d. will have been painting