They . . . . . . . . . . . . . . . . hard all day? A. shall work B. worked C. work D. has been working

The correct answer is: D. has been working

The verb “work” is in the present perfect continuous tense. This tense is used to talk about an action that started in the past and continues up to the present. In this case, the sentence is saying that the people have been working hard all day.

The other options are incorrect because they do not use the present perfect continuous tense.

• Option A, “shall work,” is in the future tense. This tense is used to talk about an action that will happen in the future.
• Option B, “worked,” is in the simple past tense. This tense is used to talk about an action that happened at a specific time in the past.
• Option C, “work,” is in the simple present tense. This tense is used to talk about an action that happens regularly or repeatedly.

I hope this explanation is helpful! Let me know if you have any other questions.