I have been __ the computer since this morning.

I have been __ the computer since this morning.

• A. at
• B. on
• C. in
• D. by

Answer: (B)

When you want to describe an activity you’ve been doing with a device for a period up to now, you use the expression be on the computer. The present perfect continuous (have been + -ing) is the right tense for something that started in the past and continues now, and since this morning marks the starting point. Using on connects the action directly to the computer, meaning you’re actively using it. At the computer would focus more on location rather than the activity, which is less natural here. In and by aren’t appropriate for this sense. So the natural completion is on.

When you want to describe an activity you’ve been doing with a device for a period up to now, you use the expression be on the computer. The present perfect continuous (have been + -ing) is the right tense for something that started in the past and continues now, and since this morning marks the starting point. Using on connects the action directly to the computer, meaning you’re actively using it. At the computer would focus more on location rather than the activity, which is less natural here. In and by aren’t appropriate for this sense. So the natural completion is on.