Select the alternative that will improve the underlined part of the sentence,…

Solution: The correct choice is "I have been working."

Why this form is needed:

• The main clause "I am tired" is in the present tense and describes a present state.

• The phrase "since 7 o'clock" indicates the action began at a specific time in the past and continues up to the present.

• To show an action that started in the past and continues now, use the present perfect continuous: Subject + have/has + been + verb-ing.

Why the other choices are incorrect:

• "I was working" uses past continuous and implies the action was in the past and does not necessarily continue to the present, so it doesn't match the present-state main clause with "since".

• "I had been working" is past perfect continuous and describes an action completed before another past event; it is incorrect because the sentence refers to the present.

• "No improvement" is wrong because the original underlined clause does not correctly express an action that started in the past and continues to now.

Final corrected sentence:

I am tired as I have been working since 7 o'clock in the morning.